SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

SCHEDULE 13D

Item 1.

Security and Issuer.

(a)

Name of Issuer:

 TriMas Corporation

(b)

Address of Issuer’s Principal Executive Offices:

 39400 Woodward Avenue, Suite 130

 Bloomfield Hills, Michigan 48304

(c)

Title and Class of Securities:

 Common Stock, par value $0.01

Item 2.

Identity and Background.

This Statement is being filed jointly on behalf of the following persons (collectively, the “Reporting Persons”):

(i)

(ii)

(iii)

(iv)

(v)

(vi)

(vii)

(viii)

Heartland Industrial Associates, L.L.C. (“Associates”);

Heartland Industrial Partners, L.P. (“HIP”);

TriMas Investment Fund I, L.L.C. (“TIF I”);

Metaldyne Investment Fund I, L.L.C. (“MIF I”);

HIP Side-By-Side Partners, L.P. (“HIP Side-By-Side”);

TriMas Investment Fund II, L.L.C. (“TIF II”);

Metaldyne Investment Fund II, L.L.C. (“MIF II”); and

HIP Side-By-Side I-A, L.L.C. (“HIP Side-By-Side I-A”).

Reporting Person

Business Address

Occupation/
Employer

Citizenship or
Jurisdiction of
Organization

Heartland Industrial Associates, L.L.C.

See below

See below

Delaware

Heartland Industrial Partners, L.P.

See below

See below

Delaware

TriMas Investment Fund I, L.L.C.

See below

See below

Delaware

Metaldyne Investment Fund I, L.L.C.

See below

See below

Delaware

HIP Side-By-Side Partners, L.P.

See below

See below

Delaware

TriMas Investment Fund II, L.L.C.

See below

See below

Delaware

Metaldyne Investment Fund II, L.L.C.

See below

See below

Delaware

HIP Side-By-Side I-A, L.L.C.

See below

See below

Delaware

Item 3.

Source and Amount of Funds or Other Consideration.

The shares of Common Stock reported herein as beneficially owned by the Reporting Persons were acquired by the Reporting Persons in a private transaction prior to the initial public offering of the Issuer, using investment capital of the Reporting Persons.  The aggregate purchase price for such shares of Common Stock was $295,545,926.00.

Item 4.

Purpose of Transaction.

On March 17, 2009, TIF I, TIF II, HIP Side-by-Side and HIP Side-by-Side I-A (collectively, the “Purchasing Parties”) entered into a Rule 10b5-1 Purchase Instruction (the “10b5-1 Purchase Plan”) with Credit Suisse Securities (USA) LLC (“Credit Suisse”) for the purpose of establishing a trading plan to effect purchases of between 1,760,000 and 3,000,000 shares of Common Stock of the Issuer in compliance with Rule 10b5-1 promulgated under the Securities Exchange Act of 1934, as amended.  The Purchasing Parties will use their working capital to finance the purchases under the 10b5-1 Purchase Plan.

Under the 10b5-1 Purchase Plan, Credit Suisse will have the authority to purchase shares of

Issuer Common Stock in the open market, at the prices and in such amounts in accordance with the terms of the 10b5-1 Purchase Plan.  The 10b5-1 Purchase Plan will permit purchases of Issuer Common Stock commencing on the 10th day after March 17, 2009 until the 10b5-1 Purchase Plan is terminated in accordance with its terms.

The purpose of the acquisition of the Common Stock pursuant to the 10b5-1 Purchase Plan is for investment. Although the Reporting Persons have no specific plan or proposal to acquire or dispose of Common Stock or other securities of the Issuer (other than pursuant to the 10b5-1 Purchase Plan, consistent with their investment purpose, the Reporting Persons, at any time and from time to time, may acquire additional Common Stock or dispose of any or all of their Common Stock or other securities of the Issuer depending upon an ongoing evaluation of the investment in the Common Stock, prevailing market conditions, other investment opportunities, liquidity requirements of the Reporting Persons, and/or other investment considerations.

Also, consistent with the investment purpose, the Reporting Persons may engage in communications with one or more shareholders of the Issuer, one or more officers or employees of the Issuer, one or more members of the board of directors of the Issuer and/or one or more representatives of the Issuer regarding the Issuer, including but not limited to its operations, business, results, plans, prospects, ownership structure and management. The Reporting Persons may discuss ideas that, if effected, may result in acquisitions by persons of additional securities of the Issuer, an extraordinary corporate transaction involving the Issuer, changes in the Issuer’s capitalization and/or changes in the board of directors or management of the Issuer.

Except as set forth in this Statement, the Reporting Persons have no plans or proposals which relate to, or could result in, any of the matters referred to in paragraphs (a) through (j), inclusive, of the instructions to Item 4 of Schedule 13D. The Reporting Persons may, at any time and from time to time, review or reconsider their position and/or change their purpose and/or formulate plans or proposals with respect thereto.

Item 5.

Interest in Securities of the Issuer.

(a)       The approximate percentages of shares of Common Stock reported as beneficially owned by the Reporting Persons is based upon 33,620,410 shares of Common Stock outstanding, as reported by the Issuer in its Annual Report on Form 10-K for the yearly period ended December 31, 2008 (as filed with the Securities and Exchange Commission on March 10, 2009).

As of the date hereof:

·      11,805,779 shares of Common Stock are owned directly by TIF I;

·      2,243,827 shares of Common Stock are owned directly by MIF I;

·      835,339 shares of Common Stock are owned directly by HIP Side-by-Side;

·      173,378 shares of Common Stock are owned directly by TIF II;

·      32,952 shares of Common Stock are owned directly by MIF II; and

·      no shares of Common Stock are owned directly by HIP Side-by-Side I-A (TIF I, MIF I, HIP Side-by-Side, TIF II, MIF II and HIP Side-by-Side I-A, collectively, the “Direct Holders”).

HIP, as the managing member of TIF I and MIF I, is an indirect beneficial owner of shares held by TIF I and MIF I.  Associates, as the managing member of TIF II, MIF II and HIP Side-by-Side I-A, and the general partner of HIP and HIP Side-by-Side, is an indirect beneficial owner of the shares held by

the Direct Holders.

(b)           Please see Items 7, 8, 9, 10, 11, and 13 for each cover sheet for each Reporting Person.  Neither the present filing nor anything contained in this item 5 shall be construed as an admission that any combination of Reporting Persons constitutes a “group” for any purpose, and each Reporting Person disclaims beneficial ownership of securities held by each other Reporting Person.

(c)           Except as set forth in Item 4 above, none of the Reporting Persons has effected any transaction in the Common Stock during the past 60 days.

(d)           Except as set forth in this Item 5, no person other than each respective record owner referred to herein of securities is known to have the right to receive or the power to direct the receipt of dividends from, or the proceeds from the sale of, such securities.

(e)           Not applicable.

Item 6.

Contracts, Arrangements, Understandings or Relationships with Respect to Securities of the Issuer

Pursuant to Rule 13d-1(k) promulgated under the Exchange Act, the Reporting Persons have entered into an agreement with respect to the joint filing of the Schedule 13D and any amendment or amendments thereto (including this filing), which agreement is deemed attached hereto as Exhibit A.

The Purchasing Parties are parties to the 10b5-1 Purchase Plan, pursuant to which Credit Suisse will purchase Common Stock of the Issuer in the open market on behalf of the Purchasing Parties.  The information contained in Item 3 of this Statement relating to the 10b5-1 Purchase Plan is incorporated herein by reference.  A copy of the 10b5-1 Purchase Plan is attached as Exhibit B hereto and incorporated herein by reference.

Certain Reporting Persons are also a party to that certain Amended and Restated Shareholders Agreement, dated as of July 19, 2002, by and among the Issuer and Metaldyne Corporation, as amended by Amendment No. 1 to the Amended and Restated Shareholders Agreement dated August 31, 2006 (the “Shareholders Agreement”).

Certain Reporting Persons are also a party to that certain Advisory Agreement, dated June 6, 2002, between HIP and the Issuer, as amended by the First Amendment to the Advisory Agreement dated November 1, 2006 between Associates and the Issuer, and as further amended by the Second Amendment to the Advisory Agreement dated November 1, 2006 between Associates and the Issuer (the “Advisory Agreement”).

The Shareholders Agreement and the Advisory Agreement are filed herewith as Exhibit C and Exhibit D, respectively, and are incorporated herein by reference.

Item 7.

Exhibits

Exhibit A

Joint Filing Agreement, dated March 18, 2009, among the Reporting Persons (filed herewith).

Exhibit B

Rule 10b5-1 Purchase Instruction by and between the Purchasing Parties and Credit Suisse dated March 17, 2009 (filed herewith).

Exhibit C

Amended and Restated Shareholders Agreement, dated as of July 19, 2002, by and among the Issuer and Metaldyne Corporation, as amended by Amendment No. 1 to the Amended and Restated Shareholders Agreement dated August 31, 2006 (incorporated herein by reference to Exhibits 10.2 and 10.3 to the Issuer’s Current Annual Report on Form 10-K, filed on March 10, 2009).

Exhibit D

Advisory Agreement, dated June 6, 2002, between HIP and the Issuer, as amended by the First Amendment to the Advisory Agreement dated November 1, 2006 between Associates and the Issuer, and as further amended by the Second Amendment to the Advisory Agreement dated November 1, 2006 between Associates and the Issuer (incorporated herein by reference to Exhibits 10.30, 10.31 and 10.32 to the Issuer’s Current Annual Report on Form 10-K, filed on March 10, 2009).

By:

  /s/ Daniel P. Tredwell

Name: Daniel P. Tredwell

Title: Managing Member

By:

  /s/ Daniel P. Tredwell

Name: Daniel P. Tredwell

Title: Managing Member

By:

  /s/ Daniel P. Tredwell

Name: Daniel P. Tredwell

Title: Managing Member

By:

  /s/ Daniel P. Tredwell

Name: Daniel P. Tredwell

Title: Managing Member

By:

  /s/ Daniel P. Tredwell

Name: Daniel P. Tredwell

Title: Managing Member

By:

  /s/ Daniel P. Tredwell

Name: Daniel P. Tredwell

Title: Managing Member

By:

  /s/ Daniel P. Tredwell

Name: Daniel P. Tredwell

Title: Managing Member

By:

  /s/ Daniel P. Tredwell

Name: Daniel P. Tredwell

Title: Managing Member

EXHIBIT A

Joint Filing Agreement, dated March 18, 2009, among the Reporting Persons (filed herewith).

EXHIBIT B

Rule 10b5-1 Purchase Instruction by and between the Purchasing Parties and Credit Suisse dated March 17, 2009 (filed herewith).

EXHIBIT C

Amended and Restated Shareholders Agreement, dated as of July 19, 2002, by and among the Issuer and Metaldyne Corporation, as amended by Amendment No. 1 to the Amended and Restated Shareholders Agreement dated August 31, 2006 (incorporated herein by reference to Exhibits 10.2 and 10.3 to the Issuer’s Current Annual Report on Form 10-K, filed on March 10, 2009).

EXHIBIT D

Advisory Agreement, dated June 6, 2002, between HIP and the Issuer, as amended by the First Amendment to the Advisory Agreement dated November 1, 2006 between Associates and the Issuer, and as further amended by the Second Amendment to the Advisory Agreement dated November 1, 2006 between Associates and the Issuer (incorporated herein by reference to Exhibits 10.30, 10.31 and 10.32 to the Issuer’s Current Annual Report on Form 10-K, filed on March 10, 2009).