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                                                                     EXHIBIT 4.F


        THIRD SUPPLEMENTAL INDENTURE dated as of December 9, 1997, between
        WYMAN-GORDON COMPANY, a Massachusetts corporation (the "Company") and
        STATE STREET BANK AND TRUST COMPANY, as trustee (the "Trustee").

        WHEREAS there has heretofore been executed and delivered to the Trustee
an Indenture dated as of March 16, 1993, amended by the Supplemental Indenture
dated as of May 19, 1994 and the Second Supplemental Indenture and Guarantee
dated as of May 27, 1994 (collectively, the "Indenture"), providing for the
issuance of the Company's 10 3/4% Senior Notes Due 2003 (the "Securities");

        WHEREAS guaranties of certain subsidiaries of the Company have been
previously released by CIT;

        WHEREAS Section 11.03 of the Indenture provides that following repayment
in full of all Indebtedness under the CIT Facility, Subsidiary Guarantors shall
be released from all obligations under Article 11 of the Indenture;

        WHEREAS the Company has delivered an officer's certificate to the
Trustee certifying compliance with Section 11.03 of the Indenture and has
requested that the Trustee deliver an appropriate instrument evidencing such
release;

        WHEREAS there are now outstanding under the Indenture, Securities in the
aggregate principal amount of $90 million;

        WHEREAS Section 9.02 of the Indenture provides that the Company and the
Trustee may amend the Indenture with the written consent of the Holders of not
less than a majority in aggregate principal amount of the Securities then
outstanding;

        WHEREAS the Company desires to amend certain provisions of the
Indenture, as set forth in Article One hereof;

        WHEREAS the Holders of at least a majority in aggregate principal amount
of the Securities outstanding have consented to the amendments effected by this
Third Supplemental Indenture; and

        WHEREAS all things necessary to make this Third Supplemental Indenture a
valid agreement, in accordance with its terms, have been done.

        NOW THEREFORE, this Third Supplemental Indenture witnesseth that, for
and in consideration of the premises, it is mutually covenanted and agreed, for
the equal and proportionate benefit of all Holders of the Securities, as
follows:


                                    ARTICLE I

                             AMENDMENTS TO INDENTURE


        SECTION 1.01  Waiver of and Amendments to Amendments to Article Four.

                (a)     The application of Sections 4.03, 4.04, 4.05, 4.06,
4.07, 4.08, 4.09, 4.10, 4.11 and 4.16 of the Indenture are hereby waived to the
extent that such provisions might otherwise interfere with the ability of the
Company and its Affiliates to enter into agreements contemplated by, and to
consummate, (i) the Offer and Consent Solicitation as set forth in the Offer to
Purchase and Consent Solicitation dated as of November 14, 1997, and any
amendments, modifications or supplements thereto (the "Offer and Consent
Solicitation") and (ii) the offer and sale of one or more new issues of senior
debt securities pursuant to the Registration






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Statement on Form S-3 (Registration No. 333-32149) filed with the Securities and
Exchange Commission by the Company and the unconditional guarantee of the
Company's obligations thereunder by its subsidiaries.

                (b)     Effective upon the date the Company accepts for purchase
and pays for all Securities validly tendered pursuant to the Offer and Consent
Solicitation (the "Payment Date"), unless, prior to that time, the Company, by
written notice to the Trustee, has terminated this Third Supplemental Indenture,
Sections 4.03, 4.04, 4.05, 4.06, 4.07, 4.08, 4.09, 4.10, 4.11 and 4.16 of the
Indenture are hereby amended by deleting all such sections and all references
thereto in their entirety, including without limitation all references, direct
or indirect, thereto in Sections 1.01, "Definitions" and 6.01, "Events of
Default Defined; Acceleration of Maturity; Waiver of Default".

        SECTION 1.02  Amendment to Article Five. Effective upon the Payment 
Date, unless, prior to that time, the Company, by written notice to the Trustee,
has terminated this Third Supplemental Indenture, Section 5.01 of the Indenture
is hereby amended to delete therefrom clauses (ii), (iii) and (iv) and all
references thereto in their entirety.

        SECTION 1.03  Amendment to Article Six. Effective upon the Payment Date,
unless, prior to that time, the Company, by written notice to the Trustee, has
terminated this Third Supplemental Indenture, Section 6.01 of the Indenture is
hereby amended to delete clauses (h) and (i), and all references thereto, in
their entirety.

        SECTION 1.04  Release of Subsidiary Guarantees. The Trustee hereby
acknowledges the release of Precision Founders, Inc., Reisner Metals, Inc.,
Sealed Composites, Inc., W-G Rome Corporation, Wyman- Gordon Composites, Inc.,
Wyman-Gordon Composite Technologies, Inc., Wyman-Gordon Fisc Limited,
Wyman-Gordon Investment Castings, Inc., and Wyman-Gordon Securities Corporation
as subsidiary guarantors pursuant to Section 11.03 of the Indenture.


                                   ARTICLE II

                                  MISCELLANEOUS

        SECTION 2.01  Instruments To Be Read Together. This Third Supplemental
Indenture is an indenture supplemental to and in implementation of the
Indenture, and said Indenture and this Third Supplemental Indenture shall
henceforth be read together.

        SECTION 2.02  Confirmation. The Indenture as amended and supplemented 
by this Third Supplemental Indenture is in all respects confirmed and preserved.

        SECTION 2.03  Terms Defined. Capitalized terms used in this Third
Supplemental Indenture and not otherwise defined herein shall have the
respective meanings set forth in the Indenture.

        SECTION 2.04  Headings. The headings of the Articles and Sections of
this Third Supplemental Indenture have been inserted for convenience of
reference only, and are not to be considered a part hereof and shall in no way
modify or restrict any of the terms and provisions hereof.

        SECTION 2.05  Governing Law. The laws of the State of New York shall
govern this Third Supplemental Indenture.

        SECTION 2.06  Counterparts. This Third Supplemental Indenture may be
executed in any number of counterparts, each of which so executed shall be
deemed to be an original, but all such counterparts shall together constitute
but one and the same instrument.



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        SECTION 2.07  Effectiveness; Termination. The provisions of this Third
Supplemental Indenture will take effect immediately upon its execution and
delivery by the Trustee in accordance with the provisions of Sections 9.02 and
9.05 of the Indenture; provided that the amendments to the Indenture set forth
in Sections 1.01, 1.02 and 1.03 of this Third Supplemental Indenture shall
become operative as specified in Sections 1.01, 1.02 and 1.03 hereof. Prior to
the Payment Date, the Company may terminate this Third Supplemental Indenture
upon written notice to the Trustee (it being understood that the Company may,
subsequent thereto, enter into a substitute third supplemental indenture).

        SECTION 2.08  Acceptance by Trustee. The Trustee accepts the amendments
to the Indenture effected by this Third Supplemental Indenture and agrees to
execute the trusts created by the Indenture as hereby amended, but only upon the
terms and conditions set forth in the Indenture.

        SECTION 2.09  Responsibility of Trustee. The recitals contained herein
shall be taken as the statements of the Company, and the Trustee assumes no
responsibility for their correctness. The Trustee makes no representations as to
the validity or sufficiency of this Third Supplemental Indenture.



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        IN WITNESS WHEREOF, the parties hereto have caused this Third
Supplemental Indenture to be duly executed, all as of the date first written
above.



                                        WYMAN-GORDON COMPANY, as Issuer



Attest:                                 By:
                                            ----------------------------------- 
                                            Name: Wallace F. Whitney, Jr.
                                            Title: Vice President, General 
                                                   Counsel and Clerk

By:
    ----------------------------------
    Alan J. Glass, Assistant Clerk


                                        WYMAN-GORDON LIMITED, as a Subsidiary 
                                        Guarantor



Attest:                                 By:
                                            ----------------------------------- 
                                            Name: Wallace F. Whitney, Jr.
                                            Title:


By:
    ----------------------------------
    Alan J. Glass, Assistant Clerk


                                        STATE STREET BANK AND TRUST COMPANY, as
                                        Trustee



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

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






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