Exhibit 5.1

		233 S. Wacker Drive, Suite 5800 Chicago, Illinois 60606 Tel: +1.312.876.7700 Fax: +1.312.993.9767 www.lw.com
		FIRM /AFFILIATE OFFICES
		Abu Dhabi		Moscow
		Barcelona		Munich
		Beijing		New Jersey
		Boston		New York
		Brussels		Orange County
		Chicago		Paris
		Doha		Riyadh
December 13, 2011		Dubai		Rome
		Frankfurt		San Diego
		Hamburg		San Francisco
		Hong Kong		Shanghai
		Houston		Silicon Valley
		London		Singapore
IDEX Corporation		Los Angeles		Tokyo
1925 West Field Court		Madrid		Washington, D.C.
Lake Forest, Illinois 60045		Milan

Ladies and Gentlemen:

We have acted as special counsel to IDEX Corporation, a Delaware corporation (the “Company”), in connection with the issuance by the Company of $350,000,000 aggregate principal amount of its 4.200% Senior Notes due 2021 (the “Notes”) under the indenture, dated as of December 6, 2010 (the “Base Indenture”), between the Company and Wells Fargo Bank, National Association, as trustee (the “Trustee”), as supplemented by the supplemental indenture, dated as of the date hereof (the “Second Supplemental Indenture” and, together with the Base Indenture, the “Indenture”), between the Company and the Trustee, and pursuant to a registration statement on Form S-3 under the Securities Act of 1933, as amended (the “Act”), filed with the Securities and Exchange Commission (the “Commission”) on December 1, 2010 (Registration No. 333-170890) (the “Registration Statement”), a base prospectus dated December 1, 2010, included in the Registration Statement at the time it originally became effective (the “Base Prospectus”), a final prospectus supplement, dated December 8, 2011, filed with the Commission pursuant to Rule 424(b) under the Act on December 9, 2011 (together with the Base Prospectus, the “Prospectus”), and the underwriting agreement, dated December 8, 2011, among J.P. Morgan Securities LLC, Merrill Lynch, Pierce, Fenner & Smith Incorporated and Wells Fargo Securities, LLC, as representatives of the several underwriters named therein, and the Company (the “Underwriting Agreement”).

This opinion is being furnished in connection with the requirements of Item 601(b)(5) of Regulation S-K under the Act, and no opinion is expressed herein as to any matter pertaining to the contents of the Registration Statement or the Prospectus, other than as expressly stated herein with respect to the issue of the Notes.

As such counsel, we have examined such matters of fact and questions of law as we have considered appropriate for purposes of this letter. With your consent, we have relied upon certificates and other assurances of officers of the Company and others as to factual matters

December 13, 2011

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without having independently verified such factual matters. We are opining herein as to the internal laws of the State of New York, and we express no opinion with respect to the applicability thereto, or the effect thereon, of the laws of any other jurisdiction or as to any matters of municipal law or the laws of any local agencies within any state.

Subject to the foregoing and the other matters set forth herein, it is our opinion that, as of the date hereof, when the Notes have been delivered against payment therefor in the manner contemplated by the Underwriting Agreement, the Notes will be legally valid and binding obligations of the Company, enforceable against the Company in accordance with their terms.

Our opinion is subject to: (i) the effect of bankruptcy, insolvency, reorganization, preference, fraudulent transfer, moratorium or other similar laws relating to or affecting the rights and remedies of creditors; (ii) the effect of general principles of equity, whether considered in a proceeding in equity or at law (including the possible unavailability of specific performance or injunctive relief), concepts of materiality, reasonableness, good faith and fair dealing, and the discretion of the court before which a proceeding is brought; (iii) the invalidity under certain circumstances under law or court decisions of provisions providing for the indemnification of or contribution to a party with respect to a liability where such indemnification or contribution is contrary to public policy; and (iv) we express no opinion as to (a) any provision for liquidated damages, default interest, late charges, monetary penalties, make-whole premiums or other economic remedies to the extent such provisions are deemed to constitute a penalty, (b) consents to, or restrictions upon, governing law, jurisdiction, venue, arbitration, remedies, or judicial relief, (c) the waiver of rights or defenses contained in Section 11.13 of the Base Indenture, (d) any provision requiring the payment of attorneys’ fees, where such payment is contrary to law or public policy, (e) any provision permitting, upon acceleration of the Notes, collection of that portion of the stated principal amount thereof which might be determined to constitute unearned interest thereon, and (f) the severability, if invalid, of provisions to the foregoing effect.

With your consent, we have assumed (a) that the Base Indenture, the Supplemental Indenture and the Notes (collectively, the “Documents”) have been duly authorized, executed and delivered by the parties thereto, (b) that each of the Documents constitutes a legally valid and binding obligation of the parties thereto other than the Company, enforceable against each of them in accordance with their respective terms, and (c) that the status of each of the Documents as legally valid and binding obligations of the parties is not be affected by any (i) breaches of, or defaults under, agreements or instruments, (ii) violations of statutes, rules, regulations or court or governmental orders, or (iii) failures to obtain required consents, approvals or authorizations from, or make required registrations, declarations or filings with, governmental authorities.

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This opinion is for your benefit in connection with the Registration Statement and may be relied upon by you and by persons entitled to rely upon it pursuant to the applicable provisions of the Act. We consent to your filing this opinion as an exhibit to the Company’s Current Report on Form 8-K, dated December 8, 2011, and to the reference to our firm contained in the Prospectus under the heading “Legal Matters.” In giving such consent, we do not thereby admit that we are in the category of persons whose consent is required under Section 7 of the Act or the rules and regulations of the Commission thereunder.