INSTRON CORP
SC 13D, 1999-05-17
MEASURING & CONTROLLING DEVICES, NEC
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<PAGE>   1
                       SECURITIES AND EXCHANGE COMMISSION
                             WASHINGTON, D.C. 20549

                                  SCHEDULE 13D
                                 (RULE 13d-101)

             INFORMATION TO BE INCLUDED IN STATEMENTS FILED PURSUANT
            TO RULE 13D-1(a) AND AMENDMENTS THERETO FILED PURSUANT TO
                                  RULE 13d-2(a)


                               Instron Corporation
- --------------------------------------------------------------------------------
                                (Name of Issuer)

                          Common Stock, $1.00 par value
- --------------------------------------------------------------------------------
                         (Title and Class of Securities)

                                    457776102
- --------------------------------------------------------------------------------
                                 (CUSIP Number)

                                Thomas N. Littman
                       Kirtland Capital Partners III L.P.
                              2550 SOM Center Road
                                    Suite 105
                          Willoughby Hills, Ohio 44094

                                  440-585-9010
- --------------------------------------------------------------------------------
   (Name, Address and Telephone Number of Person Authorized to Receive Notices
                              and Communications)

                                   May 6, 1999
- --------------------------------------------------------------------------------
             (Date of Event which Requires Filing of this Statement)

         If the filing person has previously filed a statement on Schedule 13G
to report the acquisition that is the subject of this Schedule 13D, and is
filing this schedule because of Rule 13d- 1(e), 13d-1(f) or 13d-1(g), check the
following box |_|.

         Note. Schedules filed in paper format shall include a signed original
and five copies of the Schedule including all exhibits. See Rule 13d-7(b) for
other parties to whom copies are to be sent.


                         (Continued on following pages)

                              (Page 1 of 14 Pages)


<PAGE>   2



<TABLE>
<CAPTION>
- ---------------------------------------------------------------------------------------------------------------------
CUSIP NO. 457776102                                                13D                            PAGE 2 OF 14 PAGES
- ---------------------------------------------------------------------------------------------------------------------
<S>                                                                                            <C>
     1       NAME OF REPORTING PERSONS
             S.S. OR I.R.S. IDENTIFICATION NOS. OF ABOVE PERSONS

             Kirtland Capital Partners III L.P.
- ---------------------------------------------------------------------------------------------------------------------
     2       CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP*                                       (a) [ ]
                                                                                                     (b) [X]
- ---------------------------------------------------------------------------------------------------------------------
     3       SEC USE ONLY
- ---------------------------------------------------------------------------------------------------------------------
     4       SOURCE OF FUNDS* 
             OO (See Item 3)
- ---------------------------------------------------------------------------------------------------------------------
     5       CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED
             PURSUANT TO ITEM 2(d) or 2(e)                                                               [ ]
- ---------------------------------------------------------------------------------------------------------------------
     6       CITIZENSHIP OR PLACE OF ORGANIZATION
             Ohio
- ---------------------------------------------------------------------------------------------------------------------
                   7       SOLE VOTING POWER
    NUMBER OF              0
     SHARES      ----------------------------------------------------------------------------------------------------
   BENEFICIALLY    8       SHARED VOTING POWER
     OWNED BY              1,560,115 shares Common Stock**
      EACH       ----------------------------------------------------------------------------------------------------
    REPORTING      9       SOLE DISPOSITIVE POWER
   PERSON WITH             0
                -----------------------------------------------------------------------------------------------------
                  10       SHARED DISPOSITIVE POWER
                           1,560,115 shares Common Stock**
- ---------------------------------------------------------------------------------------------------------------------
    11       AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON
             1,560,115 shares Common Stock**
- ---------------------------------------------------------------------------------------------------------------------
    12       CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES*                      [ ] 
- ---------------------------------------------------------------------------------------------------------------------
    13       PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)

             Approximately 22.5%
- ---------------------------------------------------------------------------------------------------------------------
    14       TYPE OF REPORTING PERSON*
             PN
- ---------------------------------------------------------------------------------------------------------------------
</TABLE>


                      *SEE INSTRUCTIONS BEFORE FILLING OUT!

**       Includes 42,408 shares held in Instron Corporation's Savings and
         Security Plan as of December 31, 1998.

<PAGE>   3
<TABLE>
<CAPTION>
- ---------------------------------------------------------------------------------------------------------------------
CUSIP NO. 457776102                                                13D                            PAGE 3 OF 14 PAGES
- ---------------------------------------------------------------------------------------------------------------------
<S>                                                                                            <C>
     1       NAME OF REPORTING PERSONS
             S.S. OR I.R.S. IDENTIFICATION NOS. OF ABOVE PERSONS

             ISN Acquisition Corporation
- ---------------------------------------------------------------------------------------------------------------------
     2       CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP*                                       (a) [ ]
                                                                                                     (b) [X]
- ---------------------------------------------------------------------------------------------------------------------
     3       SEC USE ONLY
- ---------------------------------------------------------------------------------------------------------------------
     4       SOURCE OF FUNDS* 
             OO (See Item 3)
- ---------------------------------------------------------------------------------------------------------------------
     5       CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED
             PURSUANT TO ITEM 2(d) or 2(e)                                                               [ ]
- ---------------------------------------------------------------------------------------------------------------------
     6       CITIZENSHIP OR PLACE OF ORGANIZATION
             Massachusetts
- ---------------------------------------------------------------------------------------------------------------------
                   7       SOLE VOTING POWER
    NUMBER OF              0
     SHARES      ----------------------------------------------------------------------------------------------------
   BENEFICIALLY    8       SHARED VOTING POWER
     OWNED BY              1,560,115 shares Common Stock**
      EACH       ----------------------------------------------------------------------------------------------------
    REPORTING      9       SOLE DISPOSITIVE POWER
   PERSON WITH             0
                -----------------------------------------------------------------------------------------------------
                  10       SHARED DISPOSITIVE POWER
                           1,560,115 shares Common Stock**
- ---------------------------------------------------------------------------------------------------------------------
    11       AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON
             1,560,115 shares Common Stock**
- ---------------------------------------------------------------------------------------------------------------------
    12       CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES*                      [ ]                
- ---------------------------------------------------------------------------------------------------------------------
    13       PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)

             Approximately 22.5%
- ---------------------------------------------------------------------------------------------------------------------
    14       TYPE OF REPORTING PERSON*
             CO
- ---------------------------------------------------------------------------------------------------------------------
</TABLE>


                      *SEE INSTRUCTIONS BEFORE FILLING OUT!

**       Includes 42,408 shares held in Instron Corporation's Savings and
         Security Plan as of December 31, 1998.

<PAGE>   4
<TABLE>
<CAPTION>
- ---------------------------------------------------------------------------------------------------------------------

CUSIP NO. 457776102                                                13D                            PAGE 4 OF 14 PAGES
- ---------------------------------------------------------------------------------------------------------------------
<S>                                                                                            <C>
     1       NAME OF REPORTING PERSONS
             S.S. OR I.R.S. IDENTIFICATION NOS. OF ABOVE PERSONS

             Kirtland Partners Ltd.
- ---------------------------------------------------------------------------------------------------------------------
     2       CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP*                                       (a) [ ]
                                                                                                     (b) [X]
- ---------------------------------------------------------------------------------------------------------------------
     3       SEC USE ONLY
- ---------------------------------------------------------------------------------------------------------------------
     4       SOURCE OF FUNDS* 
             OO (See Item 3)
- ---------------------------------------------------------------------------------------------------------------------
     5       CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED
             PURSUANT TO ITEM 2(d) or 2(e)                                                               [ ]     
- ---------------------------------------------------------------------------------------------------------------------
     6       CITIZENSHIP OR PLACE OF ORGANIZATION
             Ohio
- ---------------------------------------------------------------------------------------------------------------------
                   7       SOLE VOTING POWER
    NUMBER OF              0
     SHARES      ----------------------------------------------------------------------------------------------------
   BENEFICIALLY    8       SHARED VOTING POWER
     OWNED BY              1,560,115 shares Common Stock**
      EACH       ----------------------------------------------------------------------------------------------------
    REPORTING      9       SOLE DISPOSITIVE POWER
   PERSON WITH             0
                -----------------------------------------------------------------------------------------------------
                  10       SHARED DISPOSITIVE POWER
                           1,560,115 shares Common Stock**
- ---------------------------------------------------------------------------------------------------------------------
    11       AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON
             1,560,115 shares Common Stock**
- ---------------------------------------------------------------------------------------------------------------------
    12       CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES*                      [ ] 
- ---------------------------------------------------------------------------------------------------------------------
    13       PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)
             Approximately 22.5%
- ---------------------------------------------------------------------------------------------------------------------
    14       TYPE OF REPORTING PERSON*
             OO
- ---------------------------------------------------------------------------------------------------------------------
</TABLE>

                      *SEE INSTRUCTIONS BEFORE FILLING OUT!

**       Includes 42,408 shares held in Instron Corporation's Savings and
         Security Plan as of December 31, 1998.


<PAGE>   5
<TABLE>
<CAPTION>
- ---------------------------------------------------------------------------------------------------------------------

CUSIP NO. 457776102                                                13D                            PAGE 5 OF 14 PAGES
- ---------------------------------------------------------------------------------------------------------------------
<S>                                                                                            <C>
     1       NAME OF REPORTING PERSONS
             S.S. OR I.R.S. IDENTIFICATION NOS. OF ABOVE PERSONS

             Raymond A. Lancaster
- ---------------------------------------------------------------------------------------------------------------------
     2       CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP*                                       (a) [ ]
                                                                                                     (b) [X]
- ---------------------------------------------------------------------------------------------------------------------
     3       SEC USE ONLY
- ---------------------------------------------------------------------------------------------------------------------
     4       SOURCE OF FUNDS* 
             OO (See Item 3)
- ---------------------------------------------------------------------------------------------------------------------
     5       CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED
             PURSUANT TO ITEM 2(d) or 2(e)                                                               [ ]      
- ---------------------------------------------------------------------------------------------------------------------
     6       CITIZENSHIP OR PLACE OF ORGANIZATION
             United States
- ---------------------------------------------------------------------------------------------------------------------
                   7       SOLE VOTING POWER
    NUMBER OF              0
     SHARES      ----------------------------------------------------------------------------------------------------
   BENEFICIALLY    8       SHARED VOTING POWER
     OWNED BY              1,560,115 shares Common Stock**
      EACH       ----------------------------------------------------------------------------------------------------
    REPORTING      9       SOLE DISPOSITIVE POWER
   PERSON WITH             0
                -----------------------------------------------------------------------------------------------------
                  10       SHARED DISPOSITIVE POWER
                           1,560,115 shares Common Stock**
- ---------------------------------------------------------------------------------------------------------------------
    11       AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON
             1,560,115 shares Common Stock**
- ---------------------------------------------------------------------------------------------------------------------
    12       CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES*                      [ ]                
- ---------------------------------------------------------------------------------------------------------------------
    13       PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)
             Approximately 22.5%
- ---------------------------------------------------------------------------------------------------------------------
    14       TYPE OF REPORTING PERSON*
             IN
- ---------------------------------------------------------------------------------------------------------------------
</TABLE>

                      *SEE INSTRUCTIONS BEFORE FILLING OUT!

**       Includes 42,408 shares held in Instron Corporation's Savings and
         Security Plan as of December 31, 1998.

<PAGE>   6
<TABLE>
<CAPTION>
- ---------------------------------------------------------------------------------------------------------------------
CUSIP NO. 457776102                                                13D                            PAGE 6 OF 14 PAGES

- ---------------------------------------------------------------------------------------------------------------------
<S>                                                                                            <C>
     1       NAME OF REPORTING PERSONS
             S.S. OR I.R.S. IDENTIFICATION NOS. OF ABOVE PERSONS

             John G. Nestor
- ---------------------------------------------------------------------------------------------------------------------
     2       CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP*                                       (a) [ ]
                                                                                                     (b) [X]
- ---------------------------------------------------------------------------------------------------------------------
     3       SEC USE ONLY
- ---------------------------------------------------------------------------------------------------------------------
     4       SOURCE OF FUNDS* 
             OO (See Item 3)
- ---------------------------------------------------------------------------------------------------------------------
     5       CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED
             PURSUANT TO ITEM 2(d) or 2(e)                                                               [ ]     
- ---------------------------------------------------------------------------------------------------------------------
     6       CITIZENSHIP OR PLACE OF ORGANIZATION
             United States
- ---------------------------------------------------------------------------------------------------------------------
                   7       SOLE VOTING POWER
    NUMBER OF              0
     SHARES      ----------------------------------------------------------------------------------------------------
   BENEFICIALLY    8       SHARED VOTING POWER
     OWNED BY              1,560,115 shares Common Stock**
      EACH       ----------------------------------------------------------------------------------------------------
    REPORTING      9       SOLE DISPOSITIVE POWER
   PERSON WITH             0
                -----------------------------------------------------------------------------------------------------
                  10       SHARED DISPOSITIVE POWER
                           1,560,115 shares Common Stock**
- ---------------------------------------------------------------------------------------------------------------------
    11       AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON
             1,560,115 shares Common Stock**
- ---------------------------------------------------------------------------------------------------------------------
    12       CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES*                      [ ]
- ---------------------------------------------------------------------------------------------------------------------
    13       PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)
             Approximately 22.5%
- ---------------------------------------------------------------------------------------------------------------------
    14       TYPE OF REPORTING PERSON*
             IN
- ---------------------------------------------------------------------------------------------------------------------
</TABLE>


                      *SEE INSTRUCTIONS BEFORE FILLING OUT!

**       Includes 42,408 shares held in Instron Corporation's Savings and
         Security Plan as of December 31, 1998.

<PAGE>   7
<TABLE>
<CAPTION>
- ---------------------------------------------------------------------------------------------------------------------
CUSIP NO. 457776102                                                13D                            PAGE 7 OF 14 PAGES

- ---------------------------------------------------------------------------------------------------------------------
<S>                                                                                            <C>
     1       NAME OF REPORTING PERSONS
             S.S. OR I.R.S. IDENTIFICATION NOS. OF ABOVE PERSONS

             William R. Robertson
- ---------------------------------------------------------------------------------------------------------------------
     2       CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP*                                       (a) [ ]
                                                                                                     (b) [X]
- ---------------------------------------------------------------------------------------------------------------------
     3       SEC USE ONLY
- ---------------------------------------------------------------------------------------------------------------------
     4       SOURCE OF FUNDS* 
             OO (See Item 3)
- ---------------------------------------------------------------------------------------------------------------------
     5       CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED
             PURSUANT TO ITEM 2(d) or 2(e)                                                               [ ]      
- ---------------------------------------------------------------------------------------------------------------------
     6       CITIZENSHIP OR PLACE OF ORGANIZATION
             United States
- ---------------------------------------------------------------------------------------------------------------------
                   7       SOLE VOTING POWER
    NUMBER OF              0
     SHARES      ----------------------------------------------------------------------------------------------------
   BENEFICIALLY    8       SHARED VOTING POWER
     OWNED BY              1,560,115 shares Common Stock**
      EACH       ----------------------------------------------------------------------------------------------------
    REPORTING      9       SOLE DISPOSITIVE POWER
   PERSON WITH             0
                -----------------------------------------------------------------------------------------------------
                  10       SHARED DISPOSITIVE POWER
                           1,560,115 shares Common Stock**
- ---------------------------------------------------------------------------------------------------------------------
    11       AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON
             1,560,115 shares Common Stock
- ---------------------------------------------------------------------------------------------------------------------
    12       CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES*                      [ ]                
- ---------------------------------------------------------------------------------------------------------------------
    13       PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)
             Approximately 22.5%
- ---------------------------------------------------------------------------------------------------------------------
    14       TYPE OF REPORTING PERSON*
             IN
- ---------------------------------------------------------------------------------------------------------------------
</TABLE>

                      *SEE INSTRUCTIONS BEFORE FILLING OUT!

**       Includes 42,408 shares held in Instron Corporation's Savings and
         Security Plan as of December 31, 1998.


<PAGE>   8
<TABLE>
<CAPTION>
- ---------------------------------------------------------------------------------------------------------------------

CUSIP NO. 457776102                                                13D                            PAGE 8 OF 14 PAGES
- ---------------------------------------------------------------------------------------------------------------------
<S>                                                                                            <C>
     1       NAME OF REPORTING PERSONS
             S.S. OR I.R.S. IDENTIFICATION NOS. OF ABOVE PERSONS

             John F. Turben
- ---------------------------------------------------------------------------------------------------------------------
     2       CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP*                                       (a) [ ]
                                                                                                     (b) [X]
- ---------------------------------------------------------------------------------------------------------------------
     3       SEC USE ONLY
- ---------------------------------------------------------------------------------------------------------------------
     4       SOURCE OF FUNDS* 
             OO (See Item 3)
- ---------------------------------------------------------------------------------------------------------------------
     5       CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED
             PURSUANT TO ITEM 2(d) or 2(e)                                                               [ ]
- ---------------------------------------------------------------------------------------------------------------------
     6       CITIZENSHIP OR PLACE OF ORGANIZATION
             United States
- ---------------------------------------------------------------------------------------------------------------------
                   7       SOLE VOTING POWER
    NUMBER OF              0
     SHARES      ----------------------------------------------------------------------------------------------------
   BENEFICIALLY    8       SHARED VOTING POWER
     OWNED BY              1,560,115 shares Common Stock**
      EACH       ----------------------------------------------------------------------------------------------------
    REPORTING      9       SOLE DISPOSITIVE POWER
   PERSON WITH             0
                -----------------------------------------------------------------------------------------------------
                  10       SHARED DISPOSITIVE POWER
                           1,560,115 shares Common Stock**
- ---------------------------------------------------------------------------------------------------------------------
    11       AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON
             1,560,115 shares Common Stock**
- ---------------------------------------------------------------------------------------------------------------------
    12       CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES*                      [ ]                
- ---------------------------------------------------------------------------------------------------------------------
    13       PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)
             Approximately 22.5%
- ---------------------------------------------------------------------------------------------------------------------
    14       TYPE OF REPORTING PERSON*
             IN
- ---------------------------------------------------------------------------------------------------------------------
</TABLE>

                      *SEE INSTRUCTIONS BEFORE FILLING OUT!

**       Includes 42,408 shares held in Instron Corporation's Savings and
         Security Plan as of December 31, 1998.

<PAGE>   9




ITEM 1.  SECURITY AND ISSUER.

         This statement relates to the common stock, par value $1.00 per share
(the "Common Stock"), of Instron Corporation, a Massachusetts corporation (the
"Issuer"). The address of the Issuer's principal executive offices is 100 Royall
Street, Canton, Massachusetts 02021.

ITEM 2.  IDENTITY AND BACKGROUND.

         Kirtland Capital Partners III L.P. ("Kirtland") is an Ohio limited
partnership whose principal business is searching for, negotiating, structuring,
acquiring, holding, selling and refinancing equity interests in operating
businesses on behalf of itself and its affiliates and performing all things
incidental to or growing out of such activities. The principal business and
office address of Kirtland is 2550 SOM Center Road, Suite 105, Willoughby Hills,
Ohio 44094.

         The general partner of Kirtland is Kirtland Partners Ltd. (the "General
Partner"). The principal business and office address of the General Partner is
2550 SOM Center Road, Suite 105, Willoughby Hills, Ohio 44094. Pursuant to
General Instruction C for Schedule 13D, set forth on Schedule I hereto is
certain information regarding the controlling members of the General Partner.

         To the best of Kirtland's knowledge as of the date hereof, during the
past five years neither Kirtland nor, to the best of Kirtland's knowledge, any
of the General Partner or its members has been convicted in a criminal
proceeding (excluding traffic violations or similar misdemeanors).

         To the best of Kirtland's knowledge as of the date hereof, during the
past five years neither Kirtland nor, to the best of Kirtland's knowledge, any
of the General Partner or its members has been party to a civil proceeding of a
judicial or administrative body of competent jurisdiction and as a result of
such proceeding was or is subject to a judgment, decree or final order enjoining
future violations of, or prohibiting or mandating activities subject to, Federal
or State securities laws or finding any violation with respect to such laws.

ITEM 3.  SOURCE AND AMOUNT OF FUNDS OR OTHER CONSIDERATION.

         Kirtland may be deemed to have acquired the beneficial ownership of
1,560,115 shares of Common Stock (which includes 42,408 shares held in Instron
Corporation's Savings and Security Plan (the "401(k) Plan") as of December 31,
1998) as a result of provisions of the Voting Agreement (as defined in response
to Item 4). The shares of Common Stock to which this statement relates have not
been purchased by Kirtland, but Kirtland may be deemed to share the power to
vote and dispose such shares under the provisions of the Voting Agreement, which
is described in greater detail in response to Item 4 and such item is
incorporated herein by reference.


                                     Page 9

<PAGE>   10



ITEM 4.  PURPOSE OF TRANSACTION.

         On May 6, 1999, the Issuer, Kirtland, and ISN Acquisition Corporation,
a wholly owned subsidiary of Kirtland ("Merger Sub"), entered into an Agreement
and Plan of Merger (the "Merger Agreement"), pursuant to which Merger Sub will
merge with and into the Issuer (the "Merger"). The separate existence of Merger
Sub shall cease upon consummation of the Merger, and the Issuer will be the
surviving corporation in the Merger (the "Surviving Corporation"). At the
Effective Time (as defined in the Merger Agreement), (i) each share of Common
Stock will be converted into, and become exchangeable for, $22, and each share
of the Series B Preferred Stock of the Issuer will be converted into, and become
exchangeable for, one fully paid and non-assessable share of common stock, par
value $1.00 per share, of the Surviving Corporation, (ii) the Board of Directors
of the Issuer will be replaced by the Board of Directors of Merger Sub, (iii)
the Articles of Organization and Bylaws of the Issuer will be replaced by the
Articles of Organization and Bylaws of Merger Sub, (iv) the shares of Common
Stock will cease to be authorized for listing on the American Stock Exchange,
and (v) the shares of Common Stock will become eligible for termination of
registration pursuant to Section 12(g)(4) of the Exchange Act.

         In connection with the Merger, certain stockholders of the Issuer
holding approximately 22.5% of the outstanding shares of Common Stock have
entered into a voting agreement with Kirtland and Merger Sub (the "Voting
Agreement"), pursuant to which such stockholders have agreed, so long as the
Voting Agreement remains in effect, to (i) vote their shares of Common Stock in
favor of approval and adoption of the Merger Agreement and the Merger and (ii)
abide by certain restrictions on the transfer of shares of Common Stock owned by
each such stockholder. The Voting Agreement will terminate upon the earlier of
the consummation of the Merger or the termination of the Merger Agreement
without consummation of the Merger. Approval and adoption of the Merger
Agreement and the Merger requires the affirmative vote of the holders of
two-thirds of the outstanding shares of Common Stock.

         The purpose of the Voting Agreement is to facilitate consummation of
the Merger.

         Except as contemplated by the Merger Agreement and the Voting
Agreement, or as otherwise set forth in this Item 4, Kirtland has no present
plans or proposals which relate to or would result in:

         (a)      The acquisition by any person of additional securities of the
                  Issuer, or the disposition of securities of the Issuer;

         (b)      An extraordinary corporate transaction, such as a merger,
                  reorganization or liquidation involving the Issuer or any of
                  its subsidiaries;

         (c)      A sale or transfer of a material amount of assets of the
                  Issuer or of any of its subsidiaries;




                                     Page 10

<PAGE>   11



         (d)      Any change in the present board of directors or management of
                  the Issuer, including any plans or proposals to change the
                  number or term of directors or to fill any existing vacancies
                  on the board;

         (e)      Any material change in the capitalization or dividend policy
                  of the Issuer;

         (f)      Any other material change in the Issuer's business or
                  corporate structure;

         (g)      Changes in the Issuer's charter, bylaws or instruments
                  corresponding thereto or other actions which may impede the
                  acquisition of control of the Issuer by any other person;

         (h)      Causing the Common Stock to be delisted from the American
                  Stock Exchange;

         (i)      The Common Stock becoming eligible for termination of
                  registration pursuant to Section 12(g)(4) of the Exchange Act;
                  or

         (j)      Any action similar to any of those enumerated above.

         References to, and descriptions of, the Merger Agreement and the Voting
Agreement as set forth above in this Item 4, are qualified in their entirety by
references to the copies of the Merger Agreement, which is incorporated into
this Schedule 13D by reference, and the Voting Agreement included as Exhibit 2
to this Schedule 13D, and are incorporated in this Item 4 in their entirety
where such references and descriptions appear.

ITEM 5.  INTEREST IN SECURITIES OF THE ISSUER.

         (a) and (b) 1,560,115 shares of Common Stock (including 42,408 shares
held in the 401(k) Plan as of December 31, 1998), representing approximately
22.5% of the outstanding shares of Common Stock, based on the number of shares
of Common Stock outstanding on May 6, 1999, as represented by the Issuer, are
subject to the Voting Agreement. By virtue of the Voting Agreement, Kirtland may
be deemed to share with the respective stockholders of the Issuer party to the
Voting Agreement the power to vote or dispose the shares of Common Stock subject
to the Voting Agreement. However, Kirtland (i) is not entitled to any rights as
a stockholder of the Issuer as to the shares of Common Stock subject to the
Voting Agreement and (ii) disclaims beneficial ownership of the shares of Common
Stock of the Issuer which are covered by the Voting Agreement.

         (c) Other than as set forth in this Item 5(a)-(b), to the best of
Kirtland's knowledge as of the date hereof, there have been no transactions in
the shares of Common Stock effected during the past 60 days by Kirtland, nor to
the best of Kirtland's knowledge, by any affiliate of Kirtland or any of the
General Partner or its members.


                                     Page 11

<PAGE>   12



         (d) To the best of Kirtland's knowledge as of the date hereof, no other
person is known to have the right to receive or the power to direct the receipt
of dividends from, or the proceeds from the sale of, any shares of Common Stock.

         (e) Not applicable.

ITEM 6. CONTRACTS, ARRANGEMENTS, UNDERSTANDINGS OR RELATIONSHIPS WITH RESPECT TO
SECURITIES OF THE ISSUER.

         The information set forth or incorporated by reference in Items 3
through 5 is hereby incorporated herein by reference. A copy of the Merger
Agreement is incorporated into this Schedule 13D by reference and a copy of the
Voting Agreement is included in Exhibit 2 to this Schedule 13D.

         In connection with the Merger, Kirtland delivered to certain members of
management of the Issuer (the "Management Stockholders") a letter, dated May 6,
1999 (the "Management Letter Agreement"), and to certain other stockholders of
the Issuer (the "Other Stockholders") a letter, dated May 6, 1999 (the "Other
Stockholder Letter Agreement," together with the "Management Letter Agreement,"
the "Rollover Letters"). Following completion of the Merger, the Management
Stockholders and the Other Stockholders will maintain an equity ownership
position in the Surviving Corporation. To that end, the Rollover Letters provide
for the exchange by the Management Stockholders and Other Stockholders of
certain of their shares of Common Stock for shares of Series B Preferred Stock
of the Issuer immediately prior to the effective time of the Merger. At the
effective time of the Merger, such shares of Series B Preferred Stock will be
converted into shares of common stock, par value $1.00 per share, of the
Surviving Corporation. References to, and descriptions of, the Rollover Letters
as set forth above in this Item 6, are qualified in their entirety by references
to the copies of the Management Letter Agreement and the Other Stockholder
Letter Agreement, which are included as Exhibits 3 and 4 to this Schedule 13D,
respectively, and are incorporated in this Item 6 in their entirety where such
references and descriptions appear.

         Except as set forth in this statement, to the best of Kirtland's
knowledge as of the date hereof, there are at present no contracts,
arrangements, understandings or relationships (legal or otherwise) between
Kirtland or any persons with respect to securities of the Issuer.




                                     Page 12

<PAGE>   13



ITEM 7.  MATERIAL TO BE FILED AS EXHIBITS.

No.               Description
- ---               -----------

1        Agreement and Plan of Merger, dated as of May 6, 1999, by and among
         Instron Corporation, Kirtland Capital Partners III L.P. and ISN
         Acquisition Corporation (without exhibits) [incorporated herein by
         reference from Instron Corporation's Current Report on Form 8-K, filed
         May 11, 1999].

2        Voting Agreement, dated as of May 6, 1999, by and among Kirtland
         Capital Partners III L.P., ISN Acquisition Corporation, and the
         stockholders of Instron Corporation identified on the signature pages
         thereto.

3        Letter Agreement, dated May 6, 1999, from Kirtland Capital Partners III
         L.P. to the management stockholders of Instron Corporation identified
         on the signature pages thereto (without exhibits).

4        Letter Agreement, dated May 6, 1999, from Kirtland Capital Partners III
         L.P. to certain other stockholders of Instron Corporation identified on
         the signature pages thereto (without exhibits).




                                     Page 13

<PAGE>   14



                                    SIGNATURE

                  After reasonable inquiry and to the best of my knowledge and
belief, I certify that the information set forth in this statement is true,
complete and correct.


Date:  May 17, 1999                         By:  Kirtland Partners Ltd.,
                                                 its General Partner


                                            By:  /s/ Thomas N. Littman
                                               -----------------------------
                                            Name:  Thomas N. Littman
                                            Title: Vice President


                                    Page 14
<PAGE>   15




                                   SCHEDULE I

                        Members of Kirtland Partners Ltd.

         The following table sets forth the name, business address and present
principal occupation or employment of each controlling member of Kirtland
Partners Ltd. ("Kirtland Ltd."), the general partner of Kirtland Capital
Partners III L.P. Each such person is a U.S. citizen.



<TABLE>
<CAPTION>
           NAME              TITLE                  BUSINESS ADDRESS                  PRESENT PRINCIPAL
                                                                                         OCCUPATION
<S>                      <C>                    <C>                               <C>
Raymond A. Lancaster        Member                 2550 SOM Center Road              Executive Vice President of
                                                   Suite 105                         Kirtland Ltd.
                                                   Willoughby Hills, OH 44094

John G. Nestor              Member                 2550 SOM Center Road              President of Kirtland Ltd.
                                                   Suite 105
                                                   Willoughby Hills, OH 44094

William R. Robertson        Member                 2550 SOM Center Road              Executive Vice President of
                                                   Suite 105                         Kirtland Ltd.
                                                   Willoughby Hills, OH 44094

John F. Turben              Member                 2550 SOM Center Road              Chairman of the Board of
                                                   Suite 105                         Directors of Kirtland Ltd.
                                                   Willoughby Hills, OH 44094
</TABLE>


<PAGE>   16


                                  EXHIBIT INDEX
No.      Description
- ---      -----------

1        Agreement and Plan of Merger, dated as of May 6, 1999, by and among
         Instron Corporation, Kirtland Capital Partners III, L.P. and ISN
         Acquisition Corporation (without exhibits) [incorporated herein by
         reference from Instron Corporation's Current Report on Form 8-K, filed
         May 11, 1999].

2        Voting Agreement, dated as of May 6, 1999, by and among Kirtland
         Capital Partners III, L.P., ISN Acquisition Corporation, and the
         stockholders of Instron Corporation identified on the signature pages
         thereto.

3        Letter Agreement, dated May 6, 1999, from Kirtland Capital Partners III
         L.P. to the management stockholders of Instron Corporation identified
         on the signature pages thereto (without exhibits).

4        Letter Agreement, dated May 6, 1999, from Kirtland Capital Partners III
         L.P. to certain other stockholders of Instron Corporation identified on
         the signature pages thereto (without exhibits).








<PAGE>   1


                                                                       EXHIBIT 2

                                VOTING AGREEMENT


         AGREEMENT (the "Agreement"), dated as of May 6, 1999, among Kirtland
Capital Partners III L.P., an Ohio limited partnership ("Parent"), ISN
Acquisition Corporation, a Massachusetts corporation and a wholly owned
subsidiary of Parent ("MergerCo"), and the stockholders of Instron Corporation,
a Massachusetts corporation (the "Company"), signatory hereto (collectively
referred to herein as the "Stockholders" and each, a "Stockholder"). Capitalized
terms used and not defined herein shall have the respective meanings ascribed to
them in the Merger Agreement (as hereinafter defined).

                              W I T N E S S E T H:
                              --------------------

         WHEREAS, concurrently with the execution and delivery of this
Agreement, Parent, MergerCo and the Company have entered into an Agreement and
Plan of Merger (as such agreement may hereafter be amended from time to time,
the "Merger Agreement"), providing for the merger of MergerCo and the Company
(the "Merger");

         WHEREAS, as of the date hereof each Stockholder (i) is the owner of,
and has full rights to vote, that number of shares (the "Owned Shares") of the
Company's common stock, par value $1.00 per share (the "Common Stock"), and (ii)
is the beneficial owner of that number of shares of Common Stock (the "401(k)
Shares") held for the benefit of such Stockholder in the Instron Corporation
Savings and Security Plan (the "401(k) Plan"), set forth opposite such
Stockholder's name on Schedule I hereto (the Owned Shares, together with the
401(k) Shares, the "Existing Shares," and together with any shares acquired by
such Stockholder in any capacity after the date hereof and prior to the
termination of this Agreement whether upon the exercise of Options or by means
of purchase, dividend, distribution or otherwise (including any shares of Series
B Stock of the Company), the "Shares");

         WHEREAS, Parent desires each Stockholder to agree, and each Stockholder
is willing to agree, not to transfer or otherwise dispose of any of such
Stockholder's Shares and to vote, or to direct the voting of, the Shares in a
manner so as to facilitate consummation of the Merger, as provided herein; and

         NOW, THEREFORE, in consideration of the foregoing and the mutual
representations, warranties, covenants and agreements contained herein, the
parties hereto agree as follows:

         1.       TRANSFER OF SHARES.

                  (a) TRANSFER AND ENCUMBRANCE. Other than as provided herein or
in the Merger Agreement or those certain letter agreements of even date herewith
between the Stockholders signatory thereto and Parent (the "Rollover Letter
Agreements"), until the Expiration Date (as defined below), no Stockholder shall
hereafter (i) sell, tender, transfer, pledge, encumber, assign or otherwise
dispose of any of the Shares, (ii) deposit any Shares into a voting trust or
enter into a voting agreement or arrangement with respect to such Shares

                                        1

<PAGE>   2



or grant any proxy or power of attorney with respect thereto, (iii) enter into
any contract, option or other arrangement or undertaking with respect to the
direct or indirect sale, transfer, pledge, encumbrance, assignment or other
disposition of any Shares, or (iv) take any action that would make any
representation or warranty of such Stockholder contained herein untrue or
incorrect or have the effect of preventing or disabling such Stockholder from
performing such Stockholder's obligations under this Agreement. As used herein,
the term "Expiration Date" shall mean the earlier to occur of (A) the Effective
Time; and (B) such date and time as the Merger Agreement shall be terminated in
accordance with its terms.

                  (b) DISCLOSURE. The Stockholders hereby permit Parent and
MergerCo to publish and disclose in the Schedule 13E-3 and the Proxy Statement,
if applicable (including all documents and schedules filed with the SEC), their
identity and ownership of the Shares and the nature of their commitments,
arrangements and understandings under this Agreement.

         2.       ADDITIONAL AGREEMENTS.

                  (a) VOTING AGREEMENT. Each Stockholder shall, at any meeting
of the holders of Common Stock, however called, or in connection with any
written consent of the holders of Common Stock, vote, or shall direct the
trustee of the 401(k) Plan, in accordance with and to the extent permitted under
the terms of such plan, to vote, as applicable, the Shares, (i) in favor of the
Merger, the execution and delivery by the Company of the Merger Agreement and
the approval of the terms thereof and each of the other actions contemplated by
the Merger Agreement and this Agreement and any actions required in furtherance
thereof and hereof, and (ii) against any other Acquisition Proposal.

                  (b) NO INCONSISTENT ARRANGEMENTS. Each Stockholder hereby
covenants and agrees that, except as contemplated by this Agreement, the Merger
Agreement and the Rollover Letter Agreements, it shall not (i) transfer (which
term shall include, without limitation, any sale, gift, pledge or other
disposition), or consent to any transfer of, any or all of such Stockholder's
Shares, Options or any interest therein, (ii) enter into any contract, option or
other agreement or understanding with respect to any transfer of any or all of
such Shares, Options or any interest therein, (iii) grant any proxy,
power-of-attorney or other authorization in or with respect to such Shares or
Options, or (iv) deposit such Shares or Options into a voting trust or enter
into a voting agreement or arrangement with respect to such Shares or Options.

                  (c) NO SOLICITATION. Each Stockholder hereby agrees that such
Stockholder will not, directly or indirectly, encourage, solicit, participate in
or initiate discussions or negotiations with, or provide any information to, any
corporation, partnership, person or other entity or group (other than Parent or
any of its affiliates or representatives) concerning any other Acquisition
Proposal, except to the extent that the Company shall be so permitted pursuant
to Section 7.5 of the Merger Agreement. Each Stockholder will immediately cease
any existing activities, discussions or negotiations with any parties conducted
heretofore with

                                        2

<PAGE>   3



respect to any other Acquisition Proposal.

         3. REPRESENTATIONS AND WARRANTIES OF THE STOCKHOLDERS. Each Stockholder
hereby represents and warrants to Parent as follows:

                  (a) OWNERSHIP OF SHARES. Such Stockholder's ownership of the
Owned Shares is set forth on Schedule I. Such Stockholder is the beneficial
owner of the 401(k) Shares, as set forth on Schedule I. On the date hereof, the
Owned Shares constitute all of the Shares owned by such Stockholder. On the date
hereof, the 401(k) Shares constitute all of the Shares beneficially owned by
such Stockholder pursuant to the 401(k) Plan. Except as noted in Schedule I
hereto, such Stockholder has sole voting power and sole power to issue
instructions with respect to the matters set forth in Sections 1 and 2 hereof,
sole power of disposition, sole power of conversion and sole power to agree to
all of the matters set forth in this Agreement, in each case with respect to all
of the Owned Shares with no limitations, qualifications or restrictions on such
rights, subject to applicable securities laws, the Rollover Letter Agreements,
and the terms of this Agreement and the Merger Agreement. Such Stockholder has
the sole power to issue instructions with respect to the matters set forth in
Sections 1 and 2 hereof to the trustee of the 401(k) Plan.

                  (b) POWER; BINDING AGREEMENT. Each Stockholder has the legal
capacity, power and authority to enter into and perform all of such
Stockholder's obligations under this Agreement. The execution, delivery and
performance of this Agreement by such Stockholder will not violate any other
agreement to which such Stockholder is a party. This Agreement has been duly and
validly executed and delivered by such Stockholder and constitutes a valid and
binding agreement of such Stockholder, enforceable against such Stockholder in
accordance with its terms, subject to applicable bankruptcy or other similar
laws relating to creditors' rights and general principles of equity. There is no
beneficiary or holder of a voting trust certificate or other interest in any
trust of which such Stockholder is a trustee whose consent is required for the
execution and delivery of this Agreement or the consummation by such Stockholder
of the transactions contemplated hereby.

                  (c) NO CONFLICTS. Except for filings under the HSR Act and the
Exchange Act, (i) no filing with, and no permit, authorization, consent or
approval of, any Governmental Entity is necessary for the execution of this
Agreement by such Stockholder and the consummation by such Stockholder of the
transactions contemplated hereby and (ii) none of the execution and delivery of
this Agreement by such Stockholder, the consummation by such Stockholder of the
transactions contemplated hereby or compliance by such Stockholder with any of
the provisions hereof (A) conflicts with or results in any breach of any
organizational documents applicable to the Stockholder, (B) results in a
violation or breach of, or constitutes (with or without notice or lapse of time
or both) a default (or gives rise to any third-party right of termination,
cancellation, material modification or acceleration) under, any of the terms,
conditions or provisions of any note, loan agreement, bond, mortgage, indenture,
license, contract, commitment, arrangement, understanding, agreement or other
instrument or

                                        3

<PAGE>   4



obligation of any kind to which such Stockholder is a party or by which such
Stockholder or any of its properties or assets may be bound, or (C) violates any
order, writ, injunction, decree, judgment, statute, rule or regulation
applicable to such Stockholder or any of its properties or assets.

                  (d) NO ENCUMBRANCES. Except as set forth in Schedule I hereto
or otherwise permitted by this Agreement, the Shares and the certificates
representing such Shares are now, and at all times during the term hereof will
be, held by such Stockholder, or by a nominee or custodian or, with respect to
the 401(k) Shares, the trustee to the 401(k) Plan, for the benefit of such
Stockholder, free and clear of all Encumbrances, proxies, voting trusts or
agreements, understandings or arrangements or any other rights whatsoever,
except for any such Encumbrances set forth in Schedule I hereto or arising
hereunder, under the Merger Agreement, under the Rollover Letter Agreements and
under the terms of the 401(k) Plan.

                  (e) NO FINDER'S FEES. No broker, investment banker, financial
advisor or other person is entitled to any broker's, finder's, financial
adviser's or other similar fee or commission in connection with the transactions
contemplated hereby based upon arrangements made by or on behalf of such
Stockholder.

                  (f) RELIANCE BY PARENT. Each Stockholder understands and
acknowledges that Parent is entering into, and causing MergerCo to enter into,
the Merger Agreement in reliance upon such Stockholder's execution and delivery
of this Agreement.

         4. REPRESENTATIONS AND WARRANTIES OF PARENT AND MERGERCO. Each of
Parent and MergerCo hereby represents and warrants to the Stockholders as
follows:

                  (a) POWER; BINDING AGREEMENT. Each of Parent and MergerCo has
the corporate power and authority to enter into and perform all of its
obligations under this Agreement. The execution, delivery and performance of
this Agreement by each of Parent and MergerCo will not violate any other
agreement to which either of them is a party. This Agreement has been duly and
validly executed and delivered by each of Parent and MergerCo and constitutes a
valid and binding agreement of each of Parent and MergerCo, enforceable against
each of Parent and MergerCo in accordance with its terms.

                  (b) NO CONFLICTS. Except for filings under the HSR Act and the
Exchange Act, (i) no filing with, and no permit, authorization, consent or
approval of, any Governmental Entity is necessary for the execution of this
Agreement by each of Parent and MergerCo and the consummation by each of Parent
and MergerCo of the transactions contemplated hereby and (ii) none of the
execution and delivery of this Agreement by each of Parent and MergerCo, the
consummation by each of Parent and MergerCo of the transactions contemplated
hereby or compliance by each of Parent and MergerCo with any of the provisions
hereof (A) conflicts with or results in any breach of any organizational
documents applicable to either of Parent or MergerCo, (B) results in a violation
or breach of, or constitutes (with or without notice or

                                        4

<PAGE>   5


lapse of time or both) a default (or gives rise to any third-party right of
termination, cancellation, material modification or acceleration) under, any of
the terms, conditions or provisions of any note, loan agreement, bond, mortgage,
indenture, license, contract, commitment, arrangement, understanding, agreement
or other instrument or obligation of any kind to which either of Parent or
MergerCo is a party or by which either of Parent or MergerCo or any of their
properties or assets may be bound, or (C) violates any order, writ, injunction,
decree, judgment, statute, rule or regulation applicable to either of Parent or
MergerCo or any of their properties or assets.

         5. WAIVER OF APPRAISAL RIGHTS. Each Stockholder hereby waives his
rights under the Appraisal Rights Provisions with respect to the Shares.

         6. FURTHER ASSURANCES. From time to time, at the other party's request
and without further consideration, each party hereto shall execute and deliver
such additional documents and take all such further lawful action as may be
necessary or desirable to consummate and make effective, in the most expeditious
manner practicable, the transactions contemplated by this Agreement.

         7. STOP TRANSFER. The Stockholders shall not request that the Company
register the transfer (book-entry or otherwise) of any certificate or
uncertificated interest representing any of the Shares, unless such transfer is
made in compliance with this Agreement. In the event of a stock dividend or
distribution, or any change in the Common Stock by reason of any stock dividend,
split-up, recapitalization, combination, exchange of shares or the like, the
term "Shares" shall refer to and include the Shares as well as all such stock
dividends and distributions and any shares into which or for which any or all of
the Shares may be changed or exchanged.

         8. TERMINATION. The covenants and agreements of the Stockholders
contained in this Agreement with respect to the Shares shall terminate upon the
earlier of (a) the Effective Time and (b) the termination of the Merger
Agreement in accordance with its terms.

         9. MISCELLANEOUS.

                  (a) ENTIRE AGREEMENT. This Agreement, together with the
Rollover Letter Agreements, constitutes the entire agreement between the parties
with respect to the subject matter hereof and supersedes all other prior
agreements and understandings, both written and oral, between the parties with
respect to the subject matter hereof.

                  (b) BINDING AGREEMENT This Agreement and the obligations
hereunder shall attach to the Shares and shall be binding upon any person or
entity to which legal or beneficial ownership of such Shares shall pass, whether
by operation of law or otherwise, including, without limitation, a Stockholder's
heirs, guardians, administrators or successors. Notwithstanding any transfer of
Shares, the transferor shall remain liable for the performance

                                        5

<PAGE>   6



of all obligations of the transferor under this Agreement.

                  (c) ASSIGNMENT. This Agreement shall not be assigned by
operation of law or otherwise without the prior written consent of the other
parties, provided that Parent may assign, in its sole discretion, its rights and
obligations hereunder to any direct or indirect wholly owned Subsidiary of
Parent, but no such assignment shall relieve Parent of its obligations hereunder
if such assignee does not perform such obligations.

                  (d) AMENDMENTS, WAIVERS, ETC. This Agreement may not be
amended, changed, supplemented, waived or otherwise modified or terminated,
except upon the execution and delivery of a written agreement executed by the
parties hereto.

                  (e) NOTICES. All notices, requests, claims, demands and other
communications hereunder shall be in writing and shall be given (and shall be
deemed to have been duly received if given) by hand delivery or telecopy (with a
confirmation copy sent for next day delivery via courier service, such as
Federal Express), or by any courier service, such as Federal Express, providing
proof of delivery. All communications hereunder shall be delivered to the
respective parties at the following addresses:

         If to a Stockholder:       to such Stockholder's address set forth on 
                                    Schedule I hereto

         With a copy to:            Goodwin, Procter & Hoar  LLP
                                    Exchange Place
                                    Boston, MA  02109
                                    Attention:     Stuart M.  Cable, P.C.
                                                   Joseph L. Johnson III, P.C.
                                    Telephone No.: (617) 570-1000
                                    Telecopy No.:  (617) 523-1231

                                    and

                                    Skadden, Arps, Slate, Meagher & Flom LLP
                                    One Beacon Street, 31st Floor
                                    Boston, MA 02108
                                    Attention:    Thomas J. Dougherty, Esq.
                                    Telephone No.: (617) 573-4820
                                    Telecopy No.:  (617) 573-4822

                                    and

                                    Bingham Dana LLP
                                    150 Federal Street
                                    Boston, MA 02110

                                        6

<PAGE>   7



                                    Attention: John R. Utzschneider, Esq.
                                    Telephone No.:(617) 951-8852
                                    Telecopy No.: (617) 951-8736

         If to a Parent or
         MergerCo:                  Kirtland Capital Partners III L.P.
                                    2550 SOM Center Road
                                    Suite 105
                                    Willoughby Hills, OH 44904
                                    Attn: Raymond A. Lancaster
                                    Telephone No.: (404) 585-9010
                                    Telecopy No.:(404) 585-9699

         With a copy to:            Jones, Day, Reavis & Pogue
                                    901 Lakeside Avenue
                                    Cleveland, OH 44114
                                    Attn: Charles W. Hardin, Esq.
                                    Telephone No.: (216) 586-7084
                                    Telecopy No.: (216) 579-0212

or to such other address as the person to whom notice is given may have
previously furnished to the others in writing in the manner set forth above.

                  (f) SEVERABILITY. Whenever possible, each provision or portion
of any provision of this Agreement will be interpreted in such manner as to be
effective and valid under applicable law but if any provision or portion of any
provision of this Agreement is held to be invalid, illegal or unenforceable in
any respect under any applicable law or rule in any jurisdiction, such
invalidity, illegality or unenforceability will not affect any other provision
or portion of any provision in such jurisdiction, and this Agreement will be
reformed, construed and enforced in such jurisdiction as if such invalid,
illegal or unenforceable provision or portion of any provision had never been
contained herein.

                  (g) SPECIFIC PERFORMANCE. Each of the parties hereto
recognizes and acknowledges that a breach by it of any covenants or agreements
contained in this Agreement will cause the other party to sustain damages for
which it would not have an adequate remedy at law for money damages, and
therefore in the event of any such breach the aggrieved party shall be entitled
to the remedy of specific performance of such covenants and agreements and
injunctive and other equitable relief in addition to any other remedy to which
it may be entitled, at law or in equity.

                  (h) REMEDIES CUMULATIVE. All rights, powers and remedies
provided under this Agreement or otherwise available in respect hereof at law or
in equity shall be cumulative and not alternative or exclusive, and the exercise
of any thereof by any party shall not preclude

                                        7

<PAGE>   8




the simultaneous or later exercise of any other such right, power or remedy by
such party.

                  (i) NO WAIVER. The failure of any party hereto to exercise any
right, power or remedy provided under this Agreement or otherwise available in
respect hereof at law or in equity, or to insist upon compliance by any other
party hereto with its obligations hereunder, and any custom or practice of the
parties at variance with the terms hereof, shall not constitute a waiver by such
party of its right to exercise any such or other right, power or remedy or to
demand such compliance.

                  (j) NO THIRD PARTY BENEFICIARIES. Subject to the provisions of
Section 9(c), this Agreement is not intended to be for the benefit of, and shall
not be enforceable by, any person or entity who or which is not a party hereto.

                  (k) CHOICE OF LAW/CONSENT TO JURISDICTION. All disputes,
claims or controversies arising out of this Agreement, or the negotiation,
validity or performance of this Agreement shall be governed by and construed in
accordance with the laws of the Commonwealth of Massachusetts without regard to
its rules of conflict of laws. Each of Parent, MergerCo and the Stockholders
hereby irrevocably and unconditionally consents to submit to the sole and
exclusive jurisdiction of the courts of the Commonwealth of Massachusetts and of
the United States District Court for the District of Massachusetts (the
"Massachusetts Courts") for any litigation arising out of or relating to this
Agreement, or the negotiation, validity or performance of this Agreement (and
agrees not to commence any litigation relating thereto except in such courts),
waives any objection to the laying of venue of any such litigation in the
Massachusetts Courts and agrees not to plead or claim in any Massachusetts Court
that such litigation brought therein has been brought in any inconvenient forum.
Each of the parties hereto agrees, (a) to the extent such party is not otherwise
subject to service of process in the Commonwealth of Massachusetts, to appoint
and maintain an agent in the Commonwealth of Massachusetts as such party's agent
for acceptance of legal process, and (b) that service of process may also be
made on such party by prepaid certified mail with a proof of mailing receipt
validated by the United States Postal Service constituting evidence of valid
service. Service made pursuant to (a) or (b) above shall have the same legal
force and effect as if served upon such party personally within the Commonwealth
of Massachusetts. For purposes of implementing the parties' agreement to appoint
and maintain an agent for service of process in the Commonwealth of
Massachusetts, each such party does hereby appoint CT Corporation, 2 Oliver
Street, Boston, Massachusetts 02109, as such agent.

                  (l) DESCRIPTIVE HEADINGS. The descriptive headings used herein
are inserted for convenience of reference only and are not intended to be part
of or to affect the meaning or interpretation of this Agreement.

                  (m) COUNTERPARTS. This Agreement may be executed in
counterparts, each of which shall be deemed to be an original, but all of which,
taken together, shall constitute one and the same Agreement.

                                        8

<PAGE>   9





                  (n) NO AGREEMENT UNTIL EXECUTED. Irrespective of negotiations
among the parties or the exchanging of drafts of this Agreement, this Agreement
shall not constitute or be deemed to evidence a contract, agreement, arrangement
or understanding among the parties hereto unless and until (i) the Board of
Directors of the Company has approved, for purposes of Chapter 110F of the
Massachusetts General Laws and any applicable provision of the Company's
articles of organization, the terms of this Agreement, including, without
limitation, the voting provisions set forth in Section 2(a) of this Agreement,
and (ii) this Agreement is executed by the parties hereto.

                  (o) CONCERNING SERIES B STOCK. The Stockholders hereby
irrevocably waive any and all rights to the payment of any dividends or
distributions on the Series B Stock.


                                        9

<PAGE>   10




         IN WITNESS WHEREOF, the undersigned have caused this Agreement to be
duly executed as of the day and year first above written.




                                        KIRTLAND CAPITAL PARTNERS III L.P.

                                        By: Kirtland Partners Ltd.,
                                            its General Partner


                                        By:  /s/ Raymond A. Lancaster
                                           -----------------------------------
                                        Name:  Raymond A. Lancaster
                                        Title: 

                                        ISN ACQUISITION CORPORATION


                                        By:  /s/ Raymond A. Lancaster
                                           -----------------------------------
                                        Name:  Raymond A. Lancaster
                                        Title: President



<PAGE>   11

                                             STOCKHOLDERS:



                                             /s/ George S. Burr
                                             -----------------------------------
                                             George S. Burr



                                             /s/ Harold Hindman
                                             -----------------------------------
                                             Harold Hindman


                                             HAROLD HINDMAN TRUST



                                             By:  /s/ Robert Shapiro
                                             -----------------------------------
                                             Name: Robert Shapiro, as Trustee

                                             -and-

                                             By:  /s/ Harold Hindman
                                             -----------------------------------
                                             Name: Harold Hindman, as Trustee



                                             /s/ Joseph E. Amaral
                                             -----------------------------------
                                             Joseph E. Amaral


                                             /s/ Kenneth L. Andersen
                                             -----------------------------------
                                             Kenneth L. Andersen



                                             /s/ John R. Barrett
                                             -----------------------------------
                                             John R. Barrett



                                             /s/ Jonathan L. Burr
                                             -----------------------------------
                                             Jonathan L. Burr


                                       11

<PAGE>   12

                                          THE JONATHAN L. BURR TRUST - 1965    
                                                                               
                                                                               
                                                                               
                                          By:                                  
                                             ----------------------------------
                                          Name: Preston Saunders, as Trustee   
                                                                               
                                                                               
                                                                               
                                          /s/ Yahya Gharagozlou                
                                          -------------------------------------
                                          Yahya Gharagozlou                    
                                                                               
                                                                               
                                                                               
                                          /s/ Arthur D. Hindman                
                                          -------------------------------------
                                          Arthur D. Hindman                    
                                                                               
                                          ARTHUR D. HINDMAN TRUST              
                                                                               
                                                                               
                                                                               
                                          By: /s/ Robert Shapiro               
                                             ----------------------------------
                                          Name: Robert Shapiro, as Trustee     
                                                                               
                                                                               
                                                                               
                                          /s/ Nancy Hindman                    
                                          -------------------------------------
                                          Nancy Hindman                        
                                                                               
                                          BENJAMIN HINDMAN                     
                                                                               
                                                                               
                                                                               
                                          By: /s/ Arthur D. Hindman            
                                             ----------------------------------
                                          Name: Arthur D. Hindman, as Custodian
                                                                               


                                          SARAH HINDMAN                        
                                                                               
                                          By: /s/ Arthur D. Hindman            
                                             ----------------------------------
                                          Name: Arthur D. Hindman, as Custodian
                                                                               
                                          

                                       12

<PAGE>   13


                                    NATHANIEL HINDMAN                        
                                                                             
                                                                             
                                                                             
                                    By: Arthur D. Hindman                    
                                    ---------------------------------------  
                                    Name: Arthur D. Hindman, as Custodian    
                                                                             
                                                                             
                                                                             
                                    /s/ James M. Mcconnell                   
                                    ---------------------------------------  
                                    James M. McConnell                       
                                                                             
                                                                             
                                                                             
                                    /s/ William J. Milliken                  
                                    ---------------------------------------  
                                    William J. Milliken                      
                                                                             
                                                                             
                                                                             
                                    /s/ Linton A. Moulding                   
                                    ---------------------------------------  
                                    Linton A. Moulding                       
                                                                             
                                    LINTON A. & JANE E. MOULDING,            
                                    AS JOINT TENANTS                         
                                                                             
                                                                             
                                    By: /s/ Linton A. Moulding               
                                    ---------------------------------------  
                                    Name: Linton A. Moulding, as Joint Tenant
                                                                             
                                    -and-                                    
                                                                             
                                    By: /s/ Jane E. Moulding                 
                                    ---------------------------------------  
                                    Name: Jane E. Moulding, as Joint Tenant  
                                                                             
                                                                             
                                                                             
                                    /s/ Norman L. Smith                      
                                    ---------------------------------------  
                                    Norman L. Smith                          
                                                                             
                                                                             
                                                                             
                                    /s/ Carolyn Smith                        
                                    ---------------------------------------  
                                    Carolyn Smith                            
                                    




<PAGE>   14



                                     /s/ Helen L. Burr
                                    ---------------------------------------  
                                    Helen L. Burr









<PAGE>   15



<TABLE>
<CAPTION>
                                   Schedule I

Name and Address of Stockholders      Number of Owned Shares     Number of 401(K) Shares
- --------------------------------      ----------------------     -----------------------
<S>                                   <C>                        <C>
George S. Burr                               259,206*                       0
c/o Instron Corporation
100 Royall Street
Canton, MA 02021

Harold Hindman                               37,005**                       0
c/o Instron Corporation
100 Royall Street
Canton, MA 02021

Harold Hindman Trust                        492,814***                      0
c/o Instron Corporation
100 Royall Street
Canton, MA 02021

Joseph E. Amaral                              29,000                      4,215
c/o Instron Corporation
100 Royall Street
Canton, MA 02021

Kenneth L. Andersen                           25,328                     11,273
c/o Instron Corporation
100 Royall Street
Canton, MA 02021

John R. Barrett                               25,000                      2,553
c/o Instron Corporation
100 Royall Street
Canton, MA 02021

Jonathan L. Burr                              82,014                      3,437
c/o Instron Corporation
100 Royall Street
Canton, MA 02021
</TABLE>

- ----------------------

*      4,200 of these shares are held in street name in a cash account at Tucker
       Anthony.
**     23,775 of these shares are held in a margin account at PaineWebber
       Incorporated and 13,020 of these shares are held in street name in a
       margin account at Tucker Anthony.
***    Harold Hindman and Robert Shapiro, as Trustees, have shared voting and
       dispositive power with respect to these shares. 255,797 of these shares
       are held in street name a margin account at BT Alex. Brown Incorporated.


<PAGE>   16


<TABLE>
<S>                                   <C>                       <C>
The Jonathan L. Burr Trust - 1965      60,750                         0
c/o Instron Corporation
100 Royall Street
Canton, MA 02021

Yahya Gharagozlou                      25,000                     1,892
c/o Instron Corporation
100 Royall Street
Canton, MA 02021

Arthur D. Hindman                      34,775                     8,100
c/o Instron Corporation
100 Royall Street
Canton, MA 02021

Arthur D. Hindman Trust                15,186                         0
c/o Instron Corporation
100 Royall Street
Canton, MA 02021

Nancy Hindman                           1,000                         0
c/o Instron Corporation
100 Royall Street
Canton, MA 02021

Benjamin Hindman                       17,575                         0
c/o Instron Corporation
100 Royall Street
Canton, MA 02021

Sarah Hindman                          10,800                         0
c/o Instron Corporation
100 Royall Street
Canton, MA 02021

Nathaniel Hindman                      11,825                         0
c/o Instron Corporation
100 Royall Street
Canton, MA 02021

James M. McConnell                    211,112                     4,413
c/o Instron Corporation
100 Royall Street
Canton, MA 02021
</TABLE>


                                    

<PAGE>   17

<TABLE>
<S>                                  <C>                       <C>
William J. Milliken                    20,500                        49
c/o Instron Corporation
100 Royall Street
Canton, MA 02021

Linton A. Moulding                     25,000                     6,476
c/o Instron Corporation
100 Royall Street
Canton, MA 02021

Linton A. & Jane E. Moulding,          13,547                         0
as Joint Tenants
c/o Instron Corporation
100 Royall Street
Canton, MA 02021

Norman L. Smith                        26,720                         0
c/o Instron Corporation
100 Royall Street
Canton, MA 02021

Carolyn Smith                           2,000                         0
c/o Instron Corporation 
100 Royall Street
Canton, MA 02021

Helen L. Burr                          91,550                         0
c/o Instron Corporation
100 Royall Street
Canton, MA 02021
</TABLE>




                                    


<PAGE>   1
                                                                       Exhibit 3







                                                    May 6, 1999



To the Persons Identified
   on the Signature Page Hereto
c/o Instron Corporation
100 Royall Street
Canton, Massachusetts  02021

Gentlemen:

                  Reference is hereby made to the Agreement and Plan of Merger
(the "Merger Agreement"), dated as of May 6, 1999, among Kirtland Capital
Partners III L.P., an Ohio limited partnership ("KCP"), ISN Acquisition
Corporation, a Massachusetts corporation ("MergerCo"), and Instron Corporation,
a Massachusetts corporation (the "Company"). Capitalized terms used and not
defined herein shall have the respective meanings ascribed to them in the Merger
Agreement.

                  1. CONCERNING ROLLOVER. This letter agreement (this
"Agreement") memorializes our mutual understanding and agreement relating to the
willingness of certain members of management of the Company identified on the
signature page hereto and certain of their affiliates (collectively, the
"Management Stockholders") to maintain an equity ownership position in the
Company following the completion of the Merger. To this end, the Management
Stockholders hereby (i) agree that, from and after the date hereof and upon the
request of the Company or KCP, they will take such actions as may be reasonably
necessary to exchange the shares of Common Stock owned by them as reflected on
Exhibit A attached hereto for shares of Series B Stock as reflected on Exhibit A
attached hereto pursuant to customary documentation reasonably acceptable to
KCP, the Company and the Management Stockholders, (ii) consent to the conversion
at the Effective Time of all such shares of Series B Stock into a like number of
shares of Surviving Corporation Common Stock pursuant to customary documentation
reasonably acceptable to KCP, the Company and the Management Stockholders, and
(iii) consent to the conversion at the Effective Time of all Options identified
on Exhibit A attached hereto into the number of options identified on Exhibit A
attached hereto with the exercise price indicated thereon (such converted
options being hereinafter referred to as the "Rollover Options"). It is the
intention of the parties hereto that the rollover of stock and options described
above be structured on a tax-free basis, and the parties agree to use their
respective reasonable best efforts to attempt to give effect to such intentions.
Simultaneously with the execution and delivery hereof, KCP is entering into a
letter agreement with certain other stockholders (the "Other Stockholders") of
the Company providing for their continued participation in the equity ownership
of the Company as set forth therein (the "Other Stockholder Letter"). A fully
executed copy of the Other Stockholder Letter is being delivered to you
simultaneously herewith. KCP hereby agrees that, subject to the satisfaction of
the conditions set forth in the Merger Agreement and at the

<PAGE>   2


May 6, 1999
Page 2



Effective Time: (i) it will and will cause its affiliates to provide all of the
equity capital necessary to consummate the Transactions other than the equity
capital (a) that will be provided by the Management Stockholders as described
above and (b) that will be provided by the Other Stockholders pursuant to the
Other Stockholder Letter as in effect on the date hereof, (ii) it will and will
cause its affiliates to provide such equity capital by means of the issuance to
KCP and its affiliates of shares of Surviving Corporation Common Stock, and
(iii) the purchase price for each such share purchased by KCP and its affiliates
shall be $110 payable solely in cash.

                  2. CERTAIN AGREEMENTS. At the Effective Time, each of the
Management Stockholders and KCP will execute and deliver (and KCP will cause
each of its affiliates who are shareholders of the Company to execute and
deliver) the Stockholders Agreement in the form attached hereto as Exhibit B
(the "Stockholders Agreement"). At the Effective Time, each of the Management
Stockholders will execute and deliver a non-competition agreement in the form
attached hereto as Exhibit C. At the Effective Time, each of the Management
Stockholders (other than James M. McConnell) will execute and deliver and KCP
will cause the Company to execute and deliver an amendment to their respective
Executive Severance Agreements in the form attached hereto as Exhibit D. At the
Effective Time, Mr. McConnell will execute and deliver and KCP will cause the
Company to execute and deliver the Deferred Compensation Agreement in the form
attached hereto as Exhibit E. At the Effective Time, each of Messrs. McConnell,
Andersen, Barrett, Burr, Hindman and Gharagozlou will execute and deliver and
KCP will cause the Company to execute and deliver an amendment to their
respective Restricted Stock Award Agreements in the form attached hereto as
Exhibit F. At the Effective Time each of the Management Stockholders, the Other
Stockholders and KCP will execute and deliver (and KCP will cause (i) each of
its affiliates who are shareholders of the Company to execute and deliver and
(ii) the Company to execute and deliver) a registration rights agreement, in
customary form, providing "piggyback" registration rights for the Management
Stockholders, subject to the approval of the underwriters participating in any
particular underwritten equity offering. Notwithstanding the foregoing
provisions of this Section 2, the Jonathan Burr Trust - 1965 and Jane Elizabeth
Moulding will only enter into the Stockholders Agreement.

                  3. CONCERNING OPTIONS AND RESTRICTED STOCK. At the Effective
Time, KCP shall cause the Company to (i) adopt the Instron Corporation 1999
Stock Option Plan in the form attached hereto as Exhibit G (the "Plan"), (ii)
authorize up to 10% of the aggregate number of shares of Surviving Corporation
Common Stock outstanding on a fully diluted basis immediately following the
Effective Time (excluding any and all warrants issued to any Lender at the
Effective Time but including the Rollover Options and all options issued or
issuable under the Plan at the Effective Time) to be available for issuance
thereunder in accordance with the terms thereof, and (iii) issue options to
purchase shares of Surviving Corporation Common Stock (collectively, the "New
Options") equal to 40% of the number determined pursuant to clause (ii) hereof
to the persons and in the amounts specified on Exhibit H attached hereto, with
each such New Option to have an exercise price of $110 per share and to vest at
the rate of 20% per year or upon a Change of Control (as defined in the Plan).
All New Options issued under the Plan shall be issued in accordance with the
terms of the Plan and the terms of the Incentive Stock Option Agreement or
Nonqualified Stock


<PAGE>   3



May 6, 1999
Page 3



Option Agreement attached hereto as Exhibit I-1 and I-2 respectively. All New
Options will be "incentive stock options" to the extent permitted by law. All
Rollover Options shall be governed by the terms of the Instron Corporation 1992
Stock Incentive Plan as amended at the Effective Time as set forth on Exhibit J
attached hereto (such plan as amended being hereinafter referred to as the "1992
Plan") and the agreements governing such options except that, at the Effective
Time, all such agreements shall be amended as set forth on Exhibits K-1 and K-2
attached hereto. Shares of Common Stock that are subject to restrictions on
transfer as reflected on Exhibit A attached hereto shall, from and after the
Effective Time, be governed by the 1992 Plan and the Restricted Stock Award
Agreements, as amended in the manner contemplated hereby.

                  4. CERTAIN REPRESENTATIONS BY THE MANAGEMENT STOCKHOLDERS.
Each Management Stockholder hereby represents and warrants as follows, severally
as to such Management Stockholder only:

                           (a) Such Management Stockholder has the legal 
capacity, power and authority to enter into and perform all of its respective
obligations under this Agreement. The execution, delivery and performance of
this Agreement by such Management Stockholder will not violate any other
agreement to which such Management Stockholder is a party. This Agreement has
been duly and validly executed and delivered by such Management Stockholder and
constitutes a valid and binding agreement of such Management Stockholder,
enforceable against such Management Stockholder in accordance with its terms,
subject to applicable bankruptcy, insolvency, reorganization, moratorium,
fraudulent conveyance and other similar laws and principles of equity affecting
creditors rights and remedies generally. There is no beneficiary or holder of a
voting trust certificate or other interest in any trust of which such Management
Stockholder is a trustee whose consent is required for the execution and
delivery of this Agreement or the consummation by such Management Stockholder of
the transactions contemplated hereby, other than where any such consent has been
obtained.

                           (b)(i) Except for any filings under federal and state
securities laws and the filings referred to in Article VII of the Merger
Agreement, no filing with, and no permit, authorization, consent or approval of,
any Governmental Entity is necessary for the execution of this Agreement by such
Management Stockholder and the consummation by such Management Stockholder of
the transactions contemplated hereby and (ii) none of the execution and delivery
of this Agreement by such Management Stockholder, the consummation by such
Management Stockholder of the transactions contemplated hereby or compliance by
such Management Stockholder with any of the provisions hereof (A) results in a
violation or breach of, or constitutes (with or without notice or lapse of time
or both) a default (or gives rise to any third party right of termination,
cancellation, material modification or acceleration) under, any of the terms,
conditions or provisions of any note, loan agreement, bond, mortgage, indenture,
license, contract, commitment, arrangement, understanding, agreement or other
instrument or obligation of any kind to which such Management Stockholder is a
party or by which such Management Stockholder or any of its respective
properties or assets may be bound, of (B) violates any order, writ, injunction,
decree,


<PAGE>   4



May 6, 1999
Page 4



judgment, statute, rule or regulation applicable to such Management Stockholder
or any of its respective properties or assets.

                           (c) Such Management Stockholder understands and 
acknowledges that KCP is entering into, and causing MergerCo to enter into, the
Merger Agreement in reliance upon the execution and delivery of this Agreement
by such Management Stockholder.

                           (d) Except for the Jonathan Burr Trust - 1965, such
Management Stockholder is an "accredited investor" within the meaning of
Regulation D promulgated under the Securities Act of 1933. KCP acknowledges that
the obligations of the Jonathan Burr Trust - 1965 under Section 1 hereof shall
be subject to such trust's receipt, review and satisfaction with a private
placement memorandum or other documentation necessary to satisfy Regulation D
promulgated under the Securities Act of 1933.

                  5. CERTAIN REPRESENTATIONS BY KCP. KCP hereby represents and
warrants to the Management Stockholders as follows:

                           (a) KCP has the power and authority to enter into and
perform all of its obligations under this Agreement. The execution, delivery and
performance of this Agreement by KCP will not violate any other agreement to
which it is a party. This Agreement has been duly and validly executed and
delivered by KCP and constitutes a valid and binding agreement of KCP,
enforceable against KCP in accordance with its terms, subject to applicable
bankruptcy, insolvency, reorganization, moratorium, fraudulent conveyance and
other similar laws and principles of equity affecting creditors rights and
remedies generally.

                           (b) (i) Except for any filings under federal and 
state securities laws and the filings referred to in Article VII of the Merger
Agreement, no filing with, and no permit, authorization, consent or approval of,
any Governmental Entity is necessary for the execution of this Agreement by KCP
and the consummation by KCP of the transactions contemplated hereby and (ii)
none of the execution and delivery of this Agreement by KCP, the consummation by
KCP of the transactions contemplated hereby or compliance by KCP with any of the
provisions hereof (A) conflicts with or results in any breach of any
organizational documents applicable to KCP, (B) results in a violation or breach
of, or constitutes (with or without notice of lapse of time or both) a default
(or give rise to any third party right of termination, cancellation, material
modification or acceleration) under, any of the terms, conditions or provisions
of any note, loan agreement, bond, mortgage, indenture, license, contract,
commitment, arrangement, understanding, agreement or other instrument or
obligation of any kind to which KCP is a party or by which KCP or any of its
properties or assets may be bound, or (C) violates any order, writ, injunction,
decree, judgment, statute, rule or regulation applicable to KCP or any of its
properties or assets.

                           (c) KCP understands and acknowledges that the 
Management Stockholders are entering into this Agreement in reliance upon the
execution and delivery of the Merger Agreement by KCP.


<PAGE>   5



May 6, 1999
Page 5



                  6. FURTHER ASSURANCES. From time to time, at the other party's
request and without further consideration, each party hereto shall execute and
deliver such additional documents and take all such further lawful action as may
be reasonably necessary or desirable to consummate and make effective, in the
most expeditious manner practicable, the transactions contemplated by this
Agreement, provided that the foregoing shall not require any party hereto to
waive or amend any of its rights under this Agreement or any of the exhibits
hereto.

                  7. DEBT ARRANGEMENTS. KCP acknowledges that under the proposed
terms of the Stockholders Agreement the Company's ability to repurchase equity
of the Management Stockholders will depend on the terms of the Company's debt
arrangements. KCP agrees that it will negotiate in good faith to obtain
"baskets" under these debt arrangements in form and amounts customary for
leveraged acquisition financing agreements.

                  8. TERMINATION.  This Agreement shall terminate upon the 
termination of the Merger Agreement in accordance with its terms or upon the
execution and delivery of the Stockholders Agreement.

                  9. MISCELLANEOUS.

                           (a)      ENTIRE AGREEMENT. This Agreement (including
the Exhibits hereto) constitutes the entire agreement between the parties with
respect to the subject matter hereof and supersedes all other prior agreements
and understandings, both written and oral, between the parties with respect to
the subject matter hereof.

                           (b)      BINDING AGREEMENT.  This Agreement and the 
obligations hereunder shall be binding upon the successors and, subject to
Section 9(c) below, the assigns of the parties hereto, including, without
limitation, the heirs, guardians, administrators or successors of the Management
Stockholders.

                           (c)      ASSIGNMENT.  This Agreement shall not be
assigned without the prior written consent of the other parties.

                           (d)      AMENDMENTS, WAIVERS, ETC.  This Agreement 
may not be amended, changed, supplemented, waived or otherwise modified or
terminated, except upon the execution and delivery of a written agreement
executed by the parties hereto.

                           (e)      SEVERABILITY.  Whenever possible, each 
provision or portion of any provision of this Agreement will be interpreted in
such manner as to be effective and valid under applicable law but if any
provision or portion of any provision of this Agreement is held to be invalid,
illegal or unenforceable in any respect under any applicable law or rule in any
jurisdiction, such invalidity, illegality or unenforceability will not affect
any other provision or portion of any provision in such jurisdiction, and this
Agreement will be reformed, construed and enforced in such

<PAGE>   6



May 6, 1999
Page 6



jurisdiction as if such invalid, illegal or unenforceable provision or portion
of any provision had never been contained herein.

                           (f)      SPECIFIC PERFORMANCE.  Each of the parties
hereto recognizes and acknowledges that a breach by it of any covenants or
agreements contained in this Agreement will cause the other party to sustain
damages for which it would not have an adequate remedy at law for money damages,
and therefore in the event of any such breach the aggrieved party shall be
entitled to the remedy of specific performance of such covenants and agreements
and injunctive and other equitable relief in addition to any other remedy to
which it may be entitled, at law or in equity.

                           (g)      REMEDIES CUMULATIVE.  All rights, powers 
and remedies provided under this Agreement or otherwise available in respect
hereof at law or in equity shall be cumulative and not alternative or exclusive,
and the exercise of any thereof by any party shall not preclude the simultaneous
or later exercise of any other such right, power or remedy by such party.

                           (h)      NO WAIVER.  The failure of any party hereto
to exercise any right, power or remedy provided under this Agreement or
otherwise available in respect hereof at law or in equity, or to insist upon
compliance by any other party hereto with its obligations hereunder, and any
custom or practice of the parties at variance with the terms hereof, shall not
constitute a waiver of such party of its right to exercise any such or other
right, power or remedy or to demand such compliance.

                           (i)      NO THIRD PARTY BENEFICIARIES.  This 
Agreement is not intended to be for the benefit of, and shall not be enforceable
by, any person or entity who or which is not a party hereto.

                           (j)      CHOICE OF LAW/CONSENT TO JURISDICTION.  All
disputes, claims or controversies arising out of this Agreement, or the
negotiation, validity or performance of this Agreement shall be governed by and
construed in accordance with the laws of the Commonwealth of Massachusetts
without regard to its rules of conflict of laws. Each of the parties hereto
hereby irrevocably and unconditionally consents to submit to the sole and
exclusive jurisdiction of the courts of the Commonwealth of Massachusetts and of
the United States District Court for the District of Massachusetts (the
"Massachusetts Courts") for any litigation arising out of or relating to this
Agreement, or the negotiation, validity or performance of this Agreement (and
agrees not to commence any litigation relating thereto except in such courts),
waives any objection to the laying of venue of any such litigation in the
Massachusetts Courts and agrees not to plead or claim in any Massachusetts Court
that such litigation brought therein has been brought in any inconvenient forum.
Each of the parties hereto agrees, (a) to the extent such party is not otherwise
subject to service of process in the Commonwealth of Massachusetts, to appoint
and maintain an agent in the Commonwealth of Massachusetts as such party's agent
for acceptance of legal process, and (b) that service of process may also be
made on such party by prepaid certified mail with a proof of mailing receipt
validated by the United States Postal Service constituting evidence of valid
service. Service made pursuant to (a) or (b) above shall have the same legal
force and effect as if served upon such



<PAGE>   7



May 6, 1999
Page 7



party personally within the Commonwealth of Massachusetts. For purposes of
implementing the parties' agreement to appoint and maintain an agent for service
of process in the Commonwealth of Massachusetts, KCP does hereby appoint CT
Corporation, 2 Oliver Street, Boston, Massachusetts 02109, as such agent.

                           (k)      DESCRIPTIVE HEADINGS.  The descriptive
headings used herein are inserted for convenience of reference only and are not
intended to be part of or to affect the meaning or interpretation of this
Agreement.

                           (l)      COUNTERPARTS.  This Agreement may be 
executed in counterparts, each of which shall be deemed to be an original, but
all of which, taken together, shall constitute one and the same Agreement.

                           (m)      NO AGREEMENT UNTIL EXECUTED.  Irrespective
of negotiations among the parties or the exchanging of drafts of this Agreement,
this Agreement shall not constitute or be deemed to evidence a contract,
agreement, arrangement or understanding among the parties hereto unless and
until (i) the Board of Directors of the Company has approved, for purposes of
Chapter 110F of the Massachusetts General Laws and any applicable provision of
the Company's articles of organization, the terms of this Agreement, and (ii)
this Agreement is executed by the parties hereto.

                           (n)      ATTORNEY'S FEES.  KCP acknowledges that the
Company will be responsible for the reasonable fees and expenses of the
Management Stockholders' legal counsel in connection with the preparation and
negotiation of this Agreement and the agreements contemplated hereby up to an
aggregate of $85,000.


<PAGE>   8



May 6, 1999
Page 8



                  If the foregoing accurately sets forth our mutual
understanding and agreement, kindly sign this Agreement in the space provided
below.

                                   Very truly yours,

                                   KIRTLAND CAPITAL PARTNERS III L.P.

                                   By:      Kirtland Partners Ltd., its General
                                            Partner



                                            By: /s/ Thomas N. Littman
                                               --------------------------------
                                            Name: Thomas N. Littman
                                            Title:  Vice President

<PAGE>   9



May 6, 1999
Page 9



Accepted and Agreed this _____ day of May, 1999:

 /s/ James. M. McConell
- -----------------------------------
James M. McConnell

 /s/ Joseph E. Amaral
- -----------------------------------
Joseph E. Amaral

 /s/ Kenneth L. Andersen
- -----------------------------------
Kenneth L. Andersen

 /s/ John R. Barrett
- -----------------------------------
John R. Barrett

 /s/ Jonathan L. Burr
- -----------------------------------
Jonathan L. Burr


The Jonathan L. Burr Trust - 1965


By:
   --------------------------------
     Name:
     Title:

 /s/ Yahya Gharagozlou
- -----------------------------------
Yahya Gharagozlou


 /s/ Arthur D. Hindman
- -----------------------------------
Arthur D. Hindman


 /s/ William J. Milliken
- -----------------------------------
William J. Milliken


 /s/ Linton A. Moulding
- -----------------------------------
Linton A. Moulding


 /s/ Jane Elizabeth Moulding
- -----------------------------------
Jane Elizabeth Moulding


 /s/ Norman L. Smith
- -----------------------------------
Norman L. Smith



<PAGE>   1
                                                                       Exhibit 4





                                   May 6, 1999



George S. Burr
Helen L. Burr
The Harold Hindman Trust, dated 4/11/69
c/o Instron Corporation
100 Royall Street
Canton, Massachusetts 02021

Gentlemen:

                  Reference is hereby made to the Agreement and Plan of Merger
(the "Merger Agreement"), dated as of May 6, 1999, among Kirtland Capital
Partners III L.P., an Ohio limited partnership ("KCP"), ISN Acquisition
Corporation, a Massachusetts corporation ("MergerCo"), and Instron Corporation,
a Massachusetts corporation (the "Company"). Capitalized terms used and not
defined herein shall have the respective meanings ascribed to them in the Merger
Agreement.

                  1. CONCERNING ROLLOVER. This letter agreement (this
"Agreement") memorializes our mutual understanding and agreement relating to
your willingness to maintain an equity ownership position in the Company
following the completion of the Merger. To this end, you hereby (i) agree that,
from and after the date hereof and upon the request of the Company or KCP, you
will take such actions as may be reasonably necessary to exchange an aggregate
of, subject to Section 2, 160,000 shares of Common Stock owned by you (comprised
of 60,000 shares by Mr. Burr, 20,000 shares by Mrs. Burr and 80,000 shares by
The Harold Hindman Trust, dated 4/11/69 (the "Hindman Trust")) for an aggregate
of 32,000 shares of Series B Stock (comprised of 12,000 shares by Mr. Burr,
4,000 by Mrs. Burr and 16,000 shares by the Hindman Trust) pursuant to customary
documentation reasonably acceptable to KCP, the Company and you, and (ii)
consent to the conversion at the Effective Time of all such shares of Series B
Stock into a like number of shares of Surviving Corporation Common Stock
pursuant to customary documentation reasonably acceptable to KCP, the Company
and you. It is the intention of the parties hereto that the rollover of stock
described above be structured on a tax-free basis, and the parties agree to use
their respective reasonable best efforts to attempt to give effect to such
intentions. Simultaneously with the execution and delivery hereof, KCP is
entering into a letter agreement with certain members of management of the
Company (the "Management Stockholders") providing for their continued
participation in the equity ownership of the Company as set forth in Exhibit A
attached hereto. A fully executed copy of such letter agreement is being
delivered to you simultaneously herewith. KCP hereby agrees that, subject to the
satisfaction of the conditions set forth in the Merger Agreement, at the
Effective Time: (i) it will and will cause its affiliates to provide all of the
equity capital necessary to consummate the Transactions other than the equity
capital (a) that you will be providing as described above and (b) that will be
provided by the Management Stockholders as set forth on Exhibit A attached
hereto, (ii) it will and will cause its affiliates to provide such equity
capital by means of the issuance to KCP and its affiliates 




<PAGE>   2



George S. Burr
Helen L. Burr
The Harold Hindman Trust
May 6, 1999
Page 2

of shares of Surviving Corporation Common Stock, and (iii) the purchase price
for each such share purchased by KCP and its affiliates shall be $110 payable
solely in cash. At the Effective Time, you agree to execute and deliver the
Stockholders Agreement substantially in the form attached hereto as Exhibit B.

                  2. CERTAIN AGREEMENTS. At the Effective Time, each of you, the
Company and KCP will execute and deliver (and KCP will cause each of its
affiliates who are stockholders of the Company to execute and deliver) a
registration rights agreement, in customary form, providing "piggyback"
registration rights to you, subject to customary "cutbacks," as recommended by
the underwriters participating in any particular underwritten equity offering.
Following the date hereof, KCP and its independent accountants will consider
alternative strategies proposed by you and/or your representatives to reduce by
up to an aggregate of 50,000 shares (18,750, 6,250 and 25,000 for each of you,
respectively) the number of shares of Common Stock to be exchanged by you as
contemplated by Section 1 hereof (it being understood that, in considering any
such strategy, KCP will use its reasonable best efforts to assist in the
achievement of this objective but that KCP need not agree to any such strategy
unless KCP, its independent accountants and the Company are able to attain at
least the same level of comfort that the Merger will receive recapitalization
accounting treatment utilizing any such strategy as has been determined by KCP
and its independent accountants based on the rollover of an aggregate of 160,000
shares (60,000, 20,000 and 80,000 from each of you, respectively) of Common
Stock as contemplated in Section 1 hereof). If KCP, its independent accountants
and the Company are able to attain at least the same level of comfort as set
forth in the previous sentence to the satisfaction of each of them, then KCP and
the Company will use their reasonable best efforts to implement such strategy
and reduce the number of shares to be exchanged by you as contemplated by
Section 1 to the extent set forth in this Section 2. In the event that (i) you
do not propose any alternative strategies, (ii) your proposed alternative
strategy or strategies do not provide each of KCP, its independent accountants
and the Company with the same level of comfort as set forth above or (iii) KCP
and the Company cannot implement your proposed alternative strategy or
strategies in accordance with the previous sentence, you will participate in the
exchange as contemplated by Section 1 hereof to the full extent of the 160,000
shares (60,000, 20,000 and 80,000 from each of you, respectively) set forth
therein. You should understand that, while KCP and its independent accountants
will use their reasonable best efforts as set forth above, no assurance can be
given that such a reduction can be achieved. Each of you hereby acknowledge that
KCP is entering into the Merger Agreement on the assumption that the Merger will
qualify as a recapitalization for accounting purposes and would not have entered
into the Merger Agreement if this objective could not have been achieved.

                  3. CERTAIN REPRESENTATIONS BY YOU. Each of you hereby
represent and warrant as follows:

                           (a)      You have the legal capacity or (as
applicable) power and authority to enter into and perform all of your
obligations under this Agreement. The execution, delivery and




<PAGE>   3



George S. Burr
Helen L. Burr
The Harold Hindman Trust
May 6, 1999
Page 3



performance of this Agreement by you will not violate any other agreement to
which you are a party. This Agreement has been duly and validly executed and
delivered by you and constitutes a valid and binding agreement, enforceable
against you in accordance with its terms, subject to applicable bankruptcy,
insolvency, reorganization, moratorium, fraudulent conveyance and other similar
laws and principles of equity affecting creditors' rights and remedies
generally. There is no beneficiary or holder of a voting trust certificate or
other interest in any trust of which you are a trustee whose consent is required
for the execution and delivery of this Agreement or the consummation by you of
the transactions contemplated hereby.

                           (b)      (i)  Except for any filings under federal 
and state securities laws and the filings referred to in Article VII of the
Merger Agreement, no filing with, and no permit, authorization, consent or
approval of, any Governmental Entity is necessary for the execution of this
Agreement by you and the consummation by you of the transactions contemplated
hereby and (ii) none of the execution and delivery of this Agreement by you, the
consummation by you of the transactions contemplated hereby or compliance by you
with any of the provisions hereof (A) results in a violation or breach of, or
constitutes (with or without notice or lapse of time or both) a default (or
gives rise to any third-party right of termination, cancellation, material
modification or acceleration) under, any of the terms, conditions or provisions
of any note, loan agreement, bond, mortgage, indenture, license, contract,
commitment, arrangement, understanding, agreement or other instrument or
obligation of any kind to which you are a party or by which you or any of your
properties or assets may be bound, or (B) violates any order, writ, injunction,
decree, judgment, statute, rule or regulation applicable to you or any of your
properties or assets.

                           (c)      You understand and acknowledge that KCP is
entering into, and causing MergerCo to enter into, the Merger Agreement in
reliance upon your execution and delivery of this Agreement.

                           (d)      You are an "accredited investor" within the
meaning of Regulation D promulgated under the Securities Act of 1933, as
amended.

                  4. CERTAIN REPRESENTATIONS BY KCP. KCP hereby represents and
warrants to you as follows:

                           (a)      KCP has the power and authority to enter 
into and perform all of its obligations under this Agreement. The execution,
delivery and performance of this Agreement by KCP will not violate any other
agreement to which it is a party. This Agreement has been duly and validly
executed and delivered by KCP and constitutes a valid and binding agreement of
KCP, enforceable against KCP in accordance with its terms, subject to applicable
bankruptcy, insolvency, reorganization, moratorium, fraudulent conveyance and
other similar laws and principles of equity affecting creditors' rights and
remedies generally.


<PAGE>   4



George S. Burr
Helen L. Burr
The Harold Hindman Trust
May 6, 1999
Page 4



                           (b)      (i)  Except for any filings under federal
and state securities laws and the filings referred to in Article VII of the
Merger Agreement, no filing with, and no permit, authorization, consent or
approval of, any Governmental Entity is necessary for the execution of this
Agreement by KCP and the consummation by KCP of the transactions contemplated
hereby and (ii) none of the execution and delivery of this Agreement by KCP, the
consummation by KCP of the transactions contemplated hereby or compliance by KCP
with any of the provisions hereof (A) conflicts with or results in any breach of
any organizational documents applicable to KCP, (B) results in a violation or
breach of, or constitutes (with or without notice of lapse of time or both) a
default (or gives rise to any third-party right of termination, cancellation,
material modification or acceleration) under, any of the terms, conditions or
provisions of any note, loan agreement, bond, mortgage, indenture, license,
contract, commitment, arrangement, understanding, agreement or other instrument
or obligation of any kind to which KCP is a party or by which KCP or any of its
properties or assets may be bound, or (C) violates any order, writ, injunction,
decree, judgment, statute, rule or regulation applicable to KCP or any of its
properties or assets.

                           (c)      KCP understands and acknowledges that you 
are entering into this Agreement in reliance upon the execution and delivery of
the Merger Agreement by KCP.

                  5. FURTHER ASSURANCES. From time to time, at the other party's
request and without further consideration, each party hereto shall execute and
deliver such additional documents and take all such further lawful action as may
be reasonably necessary or desirable to consummate and make effective, in the
most expeditious manner practicable, the transactions contemplated by this
Agreement, PROVIDED that the foregoing shall not require any party hereto to
waive or amend any of its rights under this Agreement or any of the exhibits,
together with the Voting Agreement, hereto.

                  6. TERMINATION.  This Agreement shall terminate upon the 
termination of the Merger Agreement in accordance with its terms or execution
and delivery of the Stockholders Agreement.

                  7. MISCELLANEOUS.

                           (a)      ENTIRE AGREEMENT.  This Agreement (including
the Exhibits hereto) constitutes the entire agreement between the parties with
respect to the subject matter hereof and supersedes all other prior agreements
and understandings, both written and oral, between the parties with respect to
the subject matter hereof.

                           (b)      BINDING AGREEMENT.  This Agreement and the
obligations hereunder shall be binding upon the successors and, subject to
Section 7(c) below, the assigns of the parties hereto, including, without
limitation, your heirs, guardians, administrators or successors.


<PAGE>   5



George S. Burr
Helen L. Burr
The Harold Hindman Trust
May 6, 1999
Page 5



                           (c)      ASSIGNMENT.  This Agreement shall not be 
assigned without the prior written consent of the other parties.

                           (d)      AMENDMENTS, WAIVERS, ETC.  This Agreement 
may not be amended, changed, supplemented, waived or otherwise modified or
terminated, except upon the execution and delivery of a written agreement
executed by the parties hereto.

                           (e)      SEVERABILITY.  Whenever possible, each 
provision or portion of any provision of this Agreement will be interpreted in
such manner as to be effective and valid under applicable law but if any
provision or portion of any provision of this Agreement is held to be invalid,
illegal or unenforceable in any respect under any applicable law or rule in any
jurisdiction, such invalidity, illegality or unenforceability will not affect
any other provision or portion of any provision in such jurisdiction, and this
Agreement will be reformed, construed and enforced in such jurisdiction as if
such invalid, illegal or unenforceable provision or portion of any provision had
never been contained herein.

                           (f)      SPECIFIC PERFORMANCE.  Each of the parties 
hereto recognizes and acknowledges that a breach by it of any covenants or
agreements contained in this Agreement will cause the other party to sustain
damages for which it would not have an adequate remedy at law for money damages,
and therefore in the event of any such breach, the aggrieved party shall be
entitled to the remedy of specific performance of such covenants and agreements
and injunctive and other equitable relief in addition to any other remedy to
which it may be entitled, at law or in equity.

                           (g)      REMEDIES CUMULATIVE.  All rights, powers 
and remedies provided under this Agreement or otherwise available in respect
hereof at law or in equity shall be cumulative and not alternative or exclusive,
and the exercise of any thereof by any party shall not preclude the simultaneous
or later exercise of any other such right, power or remedy by such party.

                           (h)      NO WAIVER.  The failure of any party hereto
to exercise any right, power or remedy provided under this Agreement or
otherwise available in respect hereof at law or in equity, or to insist upon
compliance by any other party hereto with its obligations hereunder, and any
custom or practice of the parties at variance with the terms hereof, shall not
constitute a waiver by such party of its right to exercise any such or other
right, power or remedy or to demand such compliance.

                           (i)      NO THIRD PARTY BENEFICIARIES.  This 
Agreement is not intended to be for the benefit of, and shall not be enforceable
by, any person or entity who or which is not a party hereto.

                           (j)      CHOICE OF LAW/CONSENT TO JURISDICTION.  All
disputes, claims or controversies arising out of this Agreement, or the
negotiation, validity or performance of this




<PAGE>   6



George S. Burr
Helen L. Burr
The Harold Hindman Trust
May 6, 1999
Page 6



Agreement, shall be governed by and construed in accordance with the laws of the
Commonwealth of Massachusetts without regard to its rules of conflict of laws.
Each of the parties hereto hereby irrevocably and unconditionally consents to
submit to the sole and exclusive jurisdiction of the courts of the Commonwealth
of Massachusetts and of the United States District Court for the District of
Massachusetts (the "Massachusetts Courts") for any litigation arising out of or
relating to this Agreement, or the negotiation, validity or performance of this
Agreement (and agrees not to commence any litigation relating thereto except in
such courts), waives any objection to the laying of venue of any such litigation
in the Massachusetts Courts and agrees not to plead or claim in any
Massachusetts Court that such litigation brought therein has been brought in any
inconvenient forum. Each of the parties hereto agrees, (a) to the extent such
party is not otherwise subject to service of process in the Commonwealth of
Massachusetts, to appoint and maintain an agent in the Commonwealth of
Massachusetts as such party's agent for acceptance of legal process, and (b)
that service of process may also be made on such party by prepaid certified mail
with a proof of mailing receipt validated by the United States Postal Service
constituting evidence of valid service. Service made pursuant to (a) or (b)
above shall have the same legal force and effect as if served upon such party
personally within the Commonwealth of Massachusetts. For purposes of
implementing the parties' agreement to appoint and maintain an agent for service
of process in the Commonwealth of Massachusetts, KCP does hereby appoint CT
Corporation, 2 Oliver Street, Boston, Massachusetts 02109, as such agent.

                           (k)      DESCRIPTIVE HEADINGS.  The descriptive 
headings used herein are inserted for convenience of reference only and are not
intended to be part of or to affect the meaning or interpretation of this
Agreement.

                           (l)      COUNTERPARTS.  This Agreement may be 
executed in counterparts, each of which shall be deemed to be an original, but
all of which, taken together, shall constitute one and the same Agreement.

                           (m)      NO AGREEMENT UNTIL EXECUTED.  Irrespective
of negotiations among the parties or the exchanging of drafts of this Agreement,
this Agreement shall not constitute or be deemed to evidence a contract,
agreement, arrangement or understanding among the parties hereto unless and
until (i) the Board of Directors of the Company has approved, for purposes of
Chapter 110F of the Massachusetts General Laws and any applicable provision of
the Company's articles of organization, the terms of this Agreement, and (ii)
this Agreement is executed by the parties hereto.

                           (n)      ATTORNEY'S FEES.  KCP acknowledges that the
Company will be responsible for the reasonable fees and expenses of the Other
Stockholders' legal counsel in connection with the preparation and negotiation
of this Agreement and the agreements contemplated hereby up to an aggregate of
$40,000.



<PAGE>   7



George S. Burr
Helen L. Burr
The Harold Hindman Trust
May 6, 1999
Page 7



                  If the foregoing accurately sets forth our mutual
understanding and agreement, kindly sign this Agreement in the space provided
below.


                                   Very truly yours,

                                   KIRTLAND CAPITAL PARTNERS III L.P.

                                   By:      Kirtland Partners Ltd., its General
                                            Partner



                                            By: /s/ Thomas N. Littman
                                               -------------------------------
                                            Name:  Thomas N. Littman
                                            Title:  Vice President

<PAGE>   8



George S. Burr
Helen L. Burr
The Harold Hindman Trust
May 6, 1999
Page 8



Accepted and Agreed this _____ day of May, 1999:



 /s/ George S. Burr
- -------------------------------------
George S. Burr



 /s/ Helen S. Burr
- -------------------------------------
Helen L. Burr


THE HAROLD HINDMAN TRUST - 4/11/69


By: /s/ Harold Hindman
- -------------------------------------
         Trustee

By: /s/ Robert N. Shapiro
- -------------------------------------
         Trustee






<PAGE>   9



George S. Burr
Helen L. Burr
The Harold Hindman Trust
May 6, 1999
Page 9




INSTRON CORPORATION



By:  /s/ John R. Barrett
   ----------------------------------
Name:  John R. Barrett
Title:  Treasurer








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