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                                                                     EXHIBIT 5.1




                         [LATHAM & WATKINS LETTERHEAD]






                               September 27, 2001


IDEX Corporation
630 Dundee Road, Suite 400
Northbrook, Illinois 60062

                Re:  Registration Statement on Form S-8 with respect to 450,000
                     shares of Common Stock, par value $.01 per share

Ladies and Gentlemen:

                  In connection with the preparation and filing by IDEX
Corporation, a Delaware corporation (the "Company") with the Securities and
Exchange Commission (the "Commission") under the Securities Act of 1933, as
amended (the "Act"), of a Registration Statement on Form S-8 (the "Registration
Statement") relating to the issuance by the Company of 450,000 shares of the
Company's Common Stock, par value $.01 per share (the "Shares"), pursuant to the
1996 Stock Option Plan for Non-Officer Key Employees of IDEX Corporation (the
"Key Employees Plan"), you have requested our opinion with respect to the
matters set forth below.

                  In our capacity as your counsel in connection with such
registration, we are familiar with the proceedings taken by the Company in
connection with the authorization, issuance and sale of the Shares. In addition,
we have made such legal and factual examinations and inquiries, including an
examination of originals or copies certified or otherwise identified to our
satisfaction of such documents, corporate records and instruments, as we have
deemed necessary or appropriate for purposes of this opinion.

                  In our examination, we have assumed the genuineness of all
signatures, the authenticity of all documents submitted to us as originals and
the conformity to authentic original documents of all documents submitted to us
as copies.

                  We are opining herein as to the effect on the subject
transaction only of the General Corporation Law of the State of Delaware, and we
express no opinion with respect to the applicability thereto, or the effect
thereon, of the laws of any other jurisdiction or any other





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LATHAM & WATKINS

September 27, 2001
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Delaware laws, or as to any matters of municipal law or the laws of any local
agency within any state.

                  Subject to the foregoing, it is our opinion that the Shares
have been duly authorized and, when issued and sold upon exercise of the options
for such Shares and payment of the exercise price therefor as contemplated by
the Key Employees Plan, will be validly issued, fully paid and nonassessable.

                  We consent to your filing this opinion as an exhibit to the
Registration Statement.



                                                        Very truly yours,

                                                        /s/ Latham & Watkins

                                                        Latham & Watkins




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