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                                                                    EXHIBIT 10.2


                    FOURTH AMENDMENT AND WAIVER TO AMENDED
                    AND RESTATED REVOLVING CREDIT AGREEMENT
                    ---------------------------------------


     FOURTH AMENDMENT AND WAIVER TO AMENDED AND RESTATED REVOLVING CREDIT
AGREEMENT dated as of January 31, 2000 (this "Amendment") among OEA, INC., a
Delaware corporation (the "Company"), each of the banks named under the caption
"Banks" on the signature pages hereof (individually, a "Bank" and, collectively,
the "Banks"), BANQUE NATIONALE DE PARIS, U.S. BANK NATIONAL ASSOCIATION and
UNION BANK OF CALIFORNIA, N.A., as Co-Agents and THE NORTHERN TRUST COMPANY, as
agent for the Banks (in such capacity, together with its successors in such
capacity, the "Agent").

     WHEREAS, the Company, the Agent, the Co-Agents and the Banks have entered
into an Amended and Restated Revolving Credit Agreement dated as of April 10,
1998, as amended by a First Amendment thereto dated as of June 11, 1998, a
Second Amendment thereto dated December 10, 1998, and a Third Amendment and
Waiver thereto dated as of December 9, 1999 (as amended the "Existing
Agreement"), pursuant to which the Banks agreed to make Loans (as defined in the
Existing Agreement) to the Company in an aggregate principal amount not to
exceed $115,000,000 at any time outstanding, on and subject to the terms and
conditions thereof; and

     WHEREAS, the parties wish to amend the Existing Agreement to (a)  modify
certain covenants, and (b) waive certain Events of Default.

     NOW, THEREFORE, the parties agree as follows:


     Section 1. Definitions. Terms defined in the introductory paragraphs hereof
shall have their respective defined meanings when used in this Amendment and,
except as otherwise expressly provided herein, terms defined in the Existing
Agreement shall have their respective defined meanings when used in this
Amendment. In addition, the following terms shall have the following meanings
(terms defined in the introductory paragraphs or this Section 1 in the singular
to have correlative meanings when used in the plural and vice versa):

          "Effective Date" shall mean as of January 31, 2000, which will be
     deemed to occur upon the first date, if any, which occurs before the
     termination of this Amendment pursuant to Section 6 hereof and on which the
     conditions precedent in Section 4 shall have been satisfied.

    Section 2.  Amendments to Existing Agreement.  The following amendments are
hereby made to the Existing Agreement with effect from and after the Effective
Date:

        (a)  Section 8.3(f) of the Existing Agreement. Section 8.3(f) of the
Existing Agreement is hereby amended by adding the following before the period:

     "and grant access to, and the Company hereby grants access to the Agent and
     each Bank and their respective representatives to, any and all third party
     consultants or advisors now or hereafter retained by the Company in order
     to discuss such
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     matters and obtain such information as any Bank or the
     Agent may reasonably request."

        (b)  Section 8.5 of the Existing Agreement. Section 8.5 of the Existing
Agreement is hereby amended by (i) adding the phrase "or any substantial part
of" after the phrase "dispose of all" appearing in the introductory clause
thereof and (ii) deleting clause (c) thereof in its entirety.

        (c)  Section 8.8 of the Existing Agreement. Section 8.8 of the Existing
Agreement is hereby amended by putting a period after clause (i) of the proviso
therein and deleting everything appearing thereafter in such Section.

        (d)  Sections 8.10, 8.11, 8.12 and 8.13 of the Existing Agreement.
Sections 8.10, 8.11, 8.12 and 8.13 of the Existing Agreement are each hereby
amended as of the date hereof by adding the following at the end of each
thereof:

     "In addition, the foregoing financial test shall be measured as of March
     31, 2000 and the Company shall be in compliance therewith on March 31,
     2000.  On or before April 7, 2000, the Company shall furnish to each Bank a
     certificate of a senior financial officer of the Company (i) to the effect
     that no Default has occurred and is continuing (or, if any Default has
     occurred and is continuing, describing the same in reasonable detail and
     describing the action that the Company has taken and proposes to take with
     respect thereto) and (ii) setting forth in reasonable detail the
     computation necessary to determine whether the Company is in compliance
     with this financial covenant as of March 31, 2000."

        (e)  Section 8.18 of the Existing Agreement. Section 8.18 of the
Existing Agreement is hereby amended and restated in its entirety as follows:

        "8.18  Big Five Accounting Firm.  Upon written request of the Agent,
     the Company agrees to promptly, and in any event within ten (10) days of
     such written notice, hire, for its own account and expense, any one of the
     "Big Five" accounting firms in the Untied States, to determine, among other
     things, the enterprise value of the Company and its Subsidiaries, the on-
     going value of the Collateral and the on-going value of the Company's and
     its Subsidiaries' business systems; to prepare a written report of its
     findings addressed to the Company with a copy to the Agent and the Banks;
     and to cooperate with the Agent and the Banks with respect to such matters
     as the Agent or any Bank may reasonably request."

        (f)  Section 9(d) of the Existing Agreement. Section 9(d) of the
Existing Agreement is hereby amended by adding "or 8.18" immediately after
"8.17" appearing therein.

     Section 3.  Waiver. The Company has advised the Agent and the Banks that it
is not or has not been in compliance with Section 8.10 (Tangible Net Worth),
Section 8.11 (Indebtedness to EBITDA) and Section 8.13 (Minimum Interest
Coverage) of the Existing Agreement for its fiscal quarter ended January 31,
2000. On the Effective Date, as of and

                                      -2-
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through January 31, 2000, the Agent and the Majority Banks waive compliance by
the Company with Sections 8.10, 8.11 and 8.13. The Agent's and Majority Banks'
waiver of non-compliance with Sections 8.10, 8.11 and 8.13 of the Existing
Agreement is limited to the specific instance of failure to comply which is
described above and shall not be deemed a waiver of or consent to any other
failure to comply with the terms of Section 8.10, 8.11 or 8.13 of the Existing
Agreement or any other provisions of the Existing Agreement. Such waiver shall
not prejudice or constitute a waiver of any right or remedies which the Agent or
Banks may have or be entitled to with respect to any other breach of Section
8.10, 8.11 or 8.13 or any other provisions of the Existing Agreement.

     Section 4.  Conditions to Effective Date. The occurrence of the Effective
Date shall be subject to the satisfaction, on and as of the Effective Date, of
the following conditions precedent:

            (a)  Amendment. The Company, the Agent and the Majority Banks shall
have executed and delivered this Amendment.

            (b)  No Default. After giving effect to the waiver in Section 3
hereof, no Default or Event of Default shall have occurred and be continuing
under the Existing Agreement and the representations and warranties of the
Company in Section 7 of the Existing Agreement, as amended hereby, and in
Section 8 hereof shall be true and correct on and as of the Effective Date
(except to the extent such representations and warranties state that they relate
solely to a specified date, then as of such specified date) and the Company
shall have provided to the Agent a certificate of a senior officer of the
Company to that effect.

           (c)  Certificate of Incorporation. The Company shall have delivered
to the Agent, in form and substance satisfactory to the Agent, a certificate of
the secretary or assistant secretary of the Company (i) confirming that the
certificate of incorporation and by-laws of the Company have not been amended
since December 9, 1999 or (ii) setting forth a true and correct copy of any
amendment to the certificate of incorporation or by-laws of the Company adopted
on or after December 9, 1999.

           (d)  Company Resolutions. The Company shall have delivered to the
Agent a copy, duly certified by the secretary or an assistant secretary of the
Company, of (i) resolutions of the Company's Board of Directors authorizing or
ratifying the execution and delivery of this Amendment, and authorizing the
borrowings under the Existing Agreement, as amended hereby, (ii) all documents
evidencing other necessary corporate action, and (iii) all approvals or
consents, if any, with respect to this Amendment.

           (e)  Company Incumbency Certificate. The Company shall have delivered
to the Agent a certificate of the secretary or an assistant secretary of the
Company certifying the names of the Company's officers authorized to sign this
Amendment and all other documents or certificates to be delivered hereunder and
thereunder, together with the true signatures of such officers.

                                      -3-
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           (f)  Legal Opinion. The Company shall have delivered to the Agent an
opinion of the Company's counsel, in the form and substance satisfactory to the
Agent.

           (g)  Amendment Fee. The Company shall have paid to the Agent, for the
account of the Banks who have approved in writing the transactions contemplated
by this Amendment on or before the close of business, Chicago time, on February
17, 2000, a fee equal to the product of 10 basis points times the Commitment of
such approving Bank in effect on the Effective Date. Such fee shall be non-
refundable after February 17, 2000 unless the Majority Banks fail to sign this
Amendment.

           (h)  Other. The Company shall have delivered such other documents as
the Agent may reasonably request.

    Section 5.  Effective Date Notice.  Promptly following the occurrence of the
Effective Date, the Agent shall give notice to the parties hereto of the
occurrence of the Effective Date, which notice shall be conclusive, and all
parties may rely thereon; provided, that such notice shall not waive or
otherwise limit any right or remedy of the Agent or any Bank arising out of any
failure of any condition precedent set forth in Section 4 to be satisfied.

    Section 6.  Termination. If the Effective Date shall not have occurred on or
before February 17, 2000, the Agent on instructions of the Majority Banks may
terminate this Amendment by notice in writing to the Company at any time before
the occurrence of the Effective Date; provided, that the obligations of the
Company under Section 13 shall survive such termination.

    Section 7.  Ratification. The parties agree that the Existing Agreement, as
amended hereby, the OEA Pledge Agreement, as heretofore amended, the other
Security Documents and the Notes have not lapsed or terminated, are in full
force and effect, and are and from and after the Effective Date shall remain
binding in accordance with their terms, as amended hereby.

    Section 8.  Representations and Warranties. The Company represents and
warrants to the Agent and the Banks that:

           (a)  No Breach. The execution, delivery and performance by the
Company of this Amendment and the Existing Agreement, as amended hereby, do not
and will not conflict with or result in a breach of, or cause the creation of a
Lien (other than as contemplated by the Security Documents) or require any
consent under, the certificate of incorporation or by-laws of the Company, or
any applicable law or regulation, or any order, injunction or decree of any
court or governmental authority or agency, or any agreement or instrument to
which the Company or any of its Subsidiaries is a party or by which any of them
is bound.

           (b)  Incorporation, Corporate Power and Action, Binding Effect. The
Company has been duly incorporated and is validly existing in good standing
under the laws of the State of Delaware and has all necessary corporate power
and authority to execute, deliver and perform its obligations under this
Amendment and the Existing Agreement, as amended hereby; the execution, delivery
and performance by the Company of this Amendment and the Existing

                                      -4-
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Agreement, as amended hereby, have been duly authorized by all necessary
corporate action on its part; and this Amendment has been duly and validly
executed and delivered by the Company and constitutes a legal, valid and binding
obligation, enforceable in accordance with its terms.

           (c)  Approvals. No authorizations, approvals or consents of, and no
filings or registrations with, any governmental or regulatory authority or
agency are necessary for the execution, delivery or performance by the Company
of this Amendment, the Existing Agreement as amended hereby, or for the validity
or enforceability thereof.

    Section 9.  Certain Usages. From and after the Effective Date, each
reference to the Existing Agreement in the Existing Agreement or in any other
agreements, documents or instruments referred to or provided for in or delivered
under the Existing Agreement shall be deemed to refer to the Existing Agreement,
as amended hereby.

    Section 10.  Successors and Assigns. This Amendment and the Pledge Amendment
shall be binding upon and inure to the benefit of the Company, the Agent, the
Banks and their respective successors and assigns, except that the Company may
not transfer or assign any of its rights or interest hereunder or thereunder.

    Section 11.  Governing Law. This Amendment shall be governed by, and
construed interpreted in accordance with, the internal laws of the State of
Illinois.

    Section 12.  Counterparts. This Amendment may be executed in any number of
counterparts and any party hereto may execute any one or more of such
counterparts, all of which shall constitute one and the same instrument.
Delivery of an executed counterpart of a signature page to this Amendment by
telecopier shall be as effective as delivery of a manually executed counterpart
of this Amendment.

    Section 13.  Expenses. Whether or not the Effective Date shall occur,
without limiting the obligations of the Company under the Existing Agreement,
the Company agrees to pay, or to reimburse on demand, all reasonable costs and
expenses incurred by (i) the Agent in connection with the negotiation,
preparation, execution, delivery, modification, amendment or enforcement of this
Amendment and the other agreements, documents and instruments referred to herein
or therein, including the reasonable fees and expenses of Gardner, Carton &
Douglas, special counsel to the Agent, and (ii) any Bank in connection with
enforcement of this Amendment, the Existing Agreement as amended hereby, and the
agreements, documents and instruments referred to herein or therein, including
the reasonable fees and expenses of counsel to such Bank.

                 [Remainder of Page Intentionally Left Blank.]

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     IN WITNESS WHEREOF, the parties hereto have caused this Amendment to be
executed by their duly authorized officers as of the day and year first above
written.

                              OEA, INC.

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

                              THE NORTHERN TRUST COMPANY,
                              as Agent

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

                              THE NORTHERN TRUST COMPANY,
                              as Issuing Lender

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


                              BANKS:

                              THE NORTHERN TRUST COMPANY, individually

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

                              BANQUE NATIONALE DE PARIS, individually and as Co-
                              Agent

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

                              By:
                                 -----------------------------
                                    Name:
                                    Title:
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                              U.S. BANK NATIONAL ASSOCIATION, individually and
                              as Co-Agent

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

                              UNION BANK OF CALIFORNIA, N.A., individually and
                              as Co-Agent

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

                              CREDIT AGRICOLE INDOSUEZ, individually

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

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


                              LASALLE BANK NATIONAL ASSOCIATION, individually

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


                              GENERAL ELECTRIC CAPITAL CORPORATION, individually

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