FORM 4 Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP OF SECURITIES Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934, Section 17(a) of the Public Utility Holding Company Act of 1935 or Section 30(h) of the Investment Company Act of 1940

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1. Name and Address of Reporting Person * Genstar Capital III, L.P.   2. Issuer Name and Ticker or Trading Symbol Altra Holdings, Inc. [AIMC] 5. Relationship of Reporting Person(s) to Issuer (Check all applicable) _____ Director __X__ 10% Owner _____ Officer (give title below) _____ Other (specify below) (Last) (First) (Middle) C/O GENSTAR CAPITAL LLC, FOUR EMBARCADERO CENTER, SUITE 1900 3. Date of Earliest Transaction (Month/Day/Year) 12/15/2006 (Street) SAN FRANCISCO, CA 94111 4. If Amendment, Date Original Filed(Month/Day/Year) 6. Individual or Joint/Group Filing(Check Applicable Line) ___ Form filed by One Reporting Person _X_ Form filed by More than One Reporting Person (City) (State) (Zip) Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned

1.Title of Security (Instr. 3) 2. Transaction Date (Month/Day/Year) 2A. Deemed Execution Date, if any (Month/Day/Year) 3. Transaction Code (Instr. 8) 4. Securities Acquired (A) or Disposed of (D) (Instr. 3, 4 and 5) 5. Amount of Securities Beneficially Owned Following Reported Transaction(s) (Instr. 3 and 4) 6. Ownership Form: Direct (D) or Indirect (I) (Instr. 4) 7. Nature of Indirect Beneficial Ownership (Instr. 4) Code V Amount (A) or (D) Price Common Stock, par value $0.001 (1) (2) 12/15/2006   S   4,824,121 D $ 13.5 7,716,379 I By Genstar Capital Partners III, L.P. Common Stock, par value $0.001 (1) (2) 12/15/2006   S   173,877 D $ 13.5 2,153,609 I By Stargen III, L.P.

Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.
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Table II - Derivative Securities Acquired, Disposed of, or Beneficially Owned
(e.g., puts, calls, warrants, options, convertible securities)

1. Title of Derivative Security (Instr. 3)

2. Conversion or Exercise Price of Derivative Security

3. Transaction Date (Month/Day/Year)

3A. Deemed Execution Date, if any (Month/Day/Year)

4. Transaction Code (Instr. 8)

5. Number of Derivative Securities Acquired (A) or Disposed of (D) (Instr. 3, 4, and 5)

6. Date Exercisable and Expiration Date (Month/Day/Year)

7. Title and Amount of Underlying Securities (Instr. 3 and 4)

8. Price of Derivative Security (Instr. 5)

9. Number of Derivative Securities Beneficially Owned Following Reported Transaction(s) (Instr. 4)

10. Ownership Form of Derivative Security: Direct (D) or Indirect (I) (Instr. 4)

11. Nature of Indirect Beneficial Ownership (Instr. 4)

Code

V

(A)

(D)

Date Exercisable

Expiration Date

Title

Amount or Number of Shares

Reporting Owners

Reporting Owner Name / Address	Relationships
	Director	10% Owner	Officer	Other
Genstar Capital III, L.P. C/O GENSTAR CAPITAL LLC FOUR EMBARCADERO CENTER, SUITE 1900 SAN FRANCISCO, CA 94111		X
Genstar Capital Partners III, L.P. C/O GENSTAR CAPITAL LLC FOUR EMBARCADERO CENTER, SUITE 1900 SAN FRANCISCO, CA 94111		X
Stargen III, L.P. C/O GENSTAR CAPITAL, LLC 4 EMBARCADERO CENTER, SUITE 1900 SAN FRANCISCO, CA 94111				Non 10% Owner

Signatures

/s/ Jean-Pierre Conte, Managing Director		12/18/2006
**Signature of Reporting Person		Date

Explanation of Responses:

*	If the form is filed by more than one reporting person, see Instruction 4(b)(v).
**	Intentional misstatements or omissions of facts constitute Federal Criminal Violations. See 18 U.S.C. 1001 and 15 U.S.C. 78ff(a).
(1)	Genstar Capital III, L.P. is the sole general partner of Genstar Capital Partners III, L.P. and Stargen III, L.P.
(2)	Shares reflect conversion of preferred stock into common stock in connection with consummation of the initial public offering.
Remarks: See Exhibit 99.1 - Joint Filer Information

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