<PAGE>   1
                                                                    EXHIBIT 10.7

                      FOURTH AMENDMENT TO CREDIT AGREEMENT

          THIS FOURTH AMENDMENT TO CREDIT AGREEMENT, dated as of October 29,
1998 (this "Amendment"), is among AETNA INDUSTRIES, INC., a Delaware corporation
(the "Company"), the guarantors set forth on the signature pages hereof
(collectively, the "Guarantors"), the Lenders set forth on the signature pages
hereof (collectively, the "Lenders") and NBD BANK, a Michigan banking
corporation, as agent for the Lenders (in such capacity, the "Agent").

                                    RECITALS

          A. The Company, the Guarantors, the Agent and the Lenders are parties
to an Amended and Restated Credit Agreement dated as of April 10, 1998 (as now
and hereafter amended, the "Credit Agreement").

          B. The Company and the Guarantors desire to amend the Credit
Agreement, and the Agent and the Lenders are willing to do so in accordance with
the terms hereof.

                                      TERMS

          In consideration of the premises and of the mutual agreements herein
contained, the parties agree as follows:

          ARTICLE I. AMENDMENTS. Upon fulfillment of the conditions set forth in
Article III hereof, the Credit Agreement shall be amended as follows:

          1.1  Section 5.2(e) is restated as follows:
<PAGE>   2

               (e)  Net Worth. Permit or suffer the consolidated Net Worth of 
     the Company and its Subsidiaries to be less than the sum of: (a)(i)
     negative $19,500,000 from and including September 28, 1998 through and
     including December 27, 1998; and (ii) negative $18,500,000 thereafter, plus
     (b) 50% of Net Income, adjusted as of the last day of the fiscal quarter of
     the Company ending December 31, 1998 as calculated for the fiscal quarter
     then ending and as of each fiscal year of the Company thereafter as
     calculated for the fiscal year ending; provided, that if such Net Income is
     negative in any fiscal quarter or any fiscal year, as the case may be, the
     amount added for such period shall be zero and shall not reduce the amount
     added for any other period.

          ARTICLE II. REPRESENTATIONS. The Company and each Guarantor represent
and warrant to the Agent and the Lenders that:

          2.1  The execution, delivery and performance of this Amendment is
within its powers, has been duly authorized and is not in contravention of any
statute, law or regulation known to it or of any terms of its Articles of
Incorporation or By-laws, or of any material agreement or undertaking to which
it is a party or by which it is bound.

          2.2  This Amendment is the legal, valid and binding obligation of the
Company and each Guarantor enforceable against each in accordance with the terms
hereof. 2.3 After giving effect to the amendments contained herein, the
representations and warranties contained in Article IV of the Credit Agreement
are true on and as of the date hereof with the same force and effect as if made
on and as of the date hereof.

          2.4  After giving effect to the amendments contained herein, no Event
of Default or Default exists or has occurred and is continuing on the date
hereof. Without limiting the foregoing, no event of default or event or
condition which may become an event of default under the Senior Note Documents
has occurred or will be caused by this Amendment or any of the transactions
contemplated hereby.

          ARTICLE III. CONDITIONS OF EFFECTIVENESS. This Amendment shall not
become effective until each of the following conditions is satisfied:

<PAGE>   3


          3.1  The Company, the Guarantors and the Required Lenders shall have
signed this Amendment.

          3.2  The Company and the Guarantors shall have delivered such
resolutions, officer's certificates and legal opinions as the Agent may
reasonably request.

          3.3  The Company shall have delivered to the Agent such other 
documents and satisfied such other conditions, if any, as reasonably requested 
by the Agent.

          ARTICLE IV. MISCELLANEOUS.

          4.1  References in the Credit Agreement or in any other Loan Document
to the Credit Agreement shall be deemed to be references to the Credit Agreement
as amended hereby and as further amended from time to time.

          4.2  The Company agrees to pay and to save the Agent harmless for the
payment of all reasonable documented costs and expenses arising in connection
with this Amendment, including the reasonable documented fees of counsel to the
Agent in connection with preparing this Amendment and the related documents.

          4.3  The Company and each Guarantor acknowledge and agree that, to the
best of their knowledge, the Agent and the Lenders have fully performed all of
their obligations under all documents executed in connection with the Credit
Agreement. The Company and each Guarantor represent and warrant that they are
not aware of any claims or causes of action against the Agent or any Lender.

          4.4  Except as expressly amended hereby, the Company and each 
Guarantor agree that the Credit Agreement, the Notes, the Security Documents and
all other documents and agreements executed by the Company in connection with
the Credit Agreement in favor of the Agent or any Lender are ratified and
confirmed, as amended hereby, and shall remain in full force and effect in
accordance with their terms and that they are not aware of any set off,
counterclaim or defense with respect to any of the foregoing. Terms used but not
defined herein shall have the respective meanings ascribed thereto in the Credit
Agreement. This Amendment may be signed upon any number of counterparts with the
same effect as if the signatures thereto and hereto were upon the same
instrument, and telecopied signatures shall be effective as originals.

          4.5  The Company and the Guarantors agree to deliver to the Agent 
board resolutions approving this amendment and all transactions contemplated
hereby on or before November 30, 1998, and any failure to deliver such board
resolutions shall be an Event of Default under the Credit Agreement.

          IN WITNESS WHEREOF, the parties signing this Amendment have
caused this Amendment to be executed and delivered as of the day and year first
above written.


                             AETNA INDUSTRIES, INC.


                             By: /s/ Harold A. Brown
                                 ------------------------------
                                 Harold A. Brown

<PAGE>   4



                                 Its: Secretary, Vice President/Finance and 
                                      Chief Financial Officer


                             Guarantor
                             AETNA HOLDINGS, INC.


                             By: /s/ Harold A. Brown
                                 ------------------------------
                                 Harold A. Brown
                                 Its: Secretary, Vice President/Finance and 
                                      Chief Financial Officer


                             Guarantor
                             AETNA EXPORT SALES CORP.


                             By: /s/ Harold A. Brown
                                 ------------------------------
                                 Harold A. Brown
                                 Its:   Treasurer and Secretary


                             Guarantor
                             MS ACQUISITION CORP.


                             By: /s/ Harold A. Brown
                                 ------------------------------
                                 Harold A. Brown
                                 Its: Secretary and Vice President North America


                             Guarantor
                             AETNA MANUFACTURING CANADA LTD.


                             By: /s/ Harold A. Brown
                                 ------------------------------
                                 Harold A. Brown
                                 Its:  Treasurer and Secretary





<PAGE>   5


                             NBD BANK, as a Lender and as Agent


                             By: /s/ Thomas A. Gamm
                                 ------------------------------
                                 Thomas A. Gamm
                                 Its: Vice President


                             PNC BUSINESS CREDIT, INC.


                             By: /s/ Troy H. Bell
                                 ------------------------------

                             Its:  Assistant Vice President


                             NATIONAL BANK OF CANADA


                             By: /s/ Angie White
                                 ------------------------------

                             Its: Vice President 

                             And

                             By: /s/ Diane K. Bedad
                                 ------------------------------
                               
                             Its: Vice President


                             MICHIGAN NATIONAL BANK


                             By: /s/ Reid M. Molnar
                                 ------------------------------

                               Its: Group Manager