TRIMAS CORP

What is the purpose of the Annual Meeting?

During the Annual Meeting, holders of the Company’s Common Stock will act upon the matters outlined in the accompanying notice of Annual Meeting, including: to elect two directors to serve until the annual meeting in 2028; to ratify the appointment of Deloitte as the Company’s independent registered public accounting firm for the fiscal year ending December 31, 2025; to approve, on a non-binding advisory basis, the compensation paid to the Company’s NEOs; and to transact such other business as may properly come before the meeting. In addition, management will report on the performance of the Company and will respond to appropriate questions from shareholders.

How will the Company conduct the virtual Annual Meeting?

As permitted by Delaware law and our bylaws, we have implemented the virtual annual meeting format in order to facilitate and increase shareholder attendance and participation. In preparation for the virtual Annual Meeting (1) we will implement reasonable measures to verify that each person deemed present and permitted to vote at the meeting is a shareholder or proxy holder, (2) we will implement reasonable measures to provide shareholders and proxy holders a reasonable opportunity to participate in the meeting and to vote on matters submitted to shareholders, including an opportunity to read or hear the proceedings of the meeting substantially concurrently with such proceedings, and (3) we will maintain a record of any votes or other action taken by shareholders or proxy holders at the meeting. During the Q&A session of the meeting, we will answer appropriate submitted questions related to the business of the Annual Meeting, as time permits.

How do I attend and participate during the virtual Annual Meeting?

Our completely virtual Annual Meeting will be conducted on the internet via live webcast. You will be able to participate in the Annual Meeting online during the meeting by visitingwww.virtualshareholdermeeting.com/TRS2025. You also will be able to vote your shares electronically at the Annual Meeting.

All shareholders of record as of March 17, 2025 (the “Record Date”), or their duly appointed proxies, may participate in the Annual Meeting. To participate in the Annual Meeting, you will need the 16-digit control number included on your Notice, on your proxy card or on the instructions that accompanied your proxy materials. The Annual Meeting webcast will begin promptly at 8:00 a.m., Eastern Time, on May 14, 2025. We encourage you to access the meeting prior to the start time. Online access will begin at 7:30 a.m., Eastern Time, on May 14, 2025.

The virtual meeting platform is fully supported across internet web browsers (Internet Explorer, Microsoft Edge, Firefox, Chrome and Safari) and devices (desktops, laptops, tablets and cell phones) running the most updated version of applicable software and plugins. Participants should ensure that they have a strong Wi-Fi connection wherever they intend to participate in the meeting. Participants should also give themselves plenty of time to log in and ensure that they can hear streaming audio prior to the start of the meeting.

How do I submit questions before the virtual Annual Meeting?

Shareholders may submit questions for the Annual Meeting. If you wish to submit a question, you may do so by logging into the virtual meeting platform atwww.virtualshareholdermeeting.com/TRS2025, typing your question into the “Ask a Question” field, and clicking “Submit.” Please submit any questions before 7:45 a.m., Eastern Time, on May 14, 2025, the day of the Annual Meeting.

Appropriate questions related to the business of the Annual Meeting (the proposals being voted upon) will be answered during the Annual Meeting, subject to time constraints. Any such questions that cannot be answered during the Annual Meeting due to time constraints will be posted and answered at https://ir.trimas.com/ shareholderquestions as soon as practical after the Annual Meeting.

Additional information regarding the ability of shareholders to ask questions before the Annual Meeting, related rules of conduct and other materials for the Annual Meeting will be available atwww.virtualshareholdermeeting.com/ TRS2025.

What if I have technical difficulties during the virtual Annual Meeting?

Technical support, including related technical support phone numbers, will be available on the virtual meeting platform atwww.virtualshareholdermeeting.com/TRS2025 beginning at 7:30 a.m., Eastern Time, on May 14, 2025, through the conclusion of the Annual Meeting.

Why didn’t I receive a paper copy of this proxy statement?

We have distributed proxy materials to some of our shareholders over the internet by sending them a Notice of Internet Availability of Proxy Materials that explains how to access our proxy materials and vote online. Many other companies have transitioned to this more contemporary way of distributing annual meeting materials, often called “electronic proxy” or “Notice and Access.”

This “Notice and Access” process, expedites our shareholders’ receipt of these materials, lowers the costs of proxy solicitation and reduces the environmental impact of our annual meeting.

What if I would like to receive a paper copy of this proxy statement?

If you received a notice and would like us to send you a printed copy of our proxy materials, please follow the instructions included in your notice to request a copy.

Who is entitled to vote?

The Company’s Common Stock constitutes the voting stock of the Company. As of the Record Date, there were no outstanding shares of preferred stock of the Company. Only record holders of Common Stock at the close of business on the Record Date are entitled to receive notice of the Annual Meeting and to vote those shares of Common Stock that they held on the Record Date. Each outstanding share of Common Stock is entitled toone voteon each matter to be voted upon at the Annual Meeting. To participate in the Annual Meeting, you will need the 16-digit control number on your Notice of Internet Availability of Proxy Materials, your proxy card or on the instructions that accompanied your proxy materials. We encourage you to access the Annual Meeting before the start time of 8:00 a.m., Eastern Time, on May 14, 2025. Please allow ample time for online check-in, which will begin at 7:30 a.m., Eastern Time, on May 14, 2025.

What constitutes a quorum?

For business to be conducted at the Annual Meeting, a quorum must be present. The presence at the Annual Meeting, in person or by proxy, of the holders of a majority of the shares of Common Stock issued and outstanding and entitled to vote on the Record Date will constitute a quorum for all purposes. As of the Record Date, 40,716,445 shares of Common Stock were issued and outstanding and entitled to vote. Broker non-votes and proxies marked with abstentions or instructions to withhold votes will be counted as present in determining whether there is a quorum.

What is the difference between holding shares as a shareholder of record and being a beneficial owner?

Shareholders of Record. If, at the close of business on the Record Date, your shares are registered directly in your name with the Company’s transfer agent, Computershare, you are considered the shareholder of record with respect to those shares, and these proxy materials (including a proxy card) are being sent directly to you by the Company. As a shareholder of record, you have the right to grant your voting proxy directly to the Company via the proxy card or to vote electronically during the Annual Meeting.

Beneficial Owners. If, at the close of business on the Record Date, your shares were not issued directly in your name, but were held in a stock brokerage account or by a bank, trustee or other nominee, you are considered the beneficial owner of shares, and these proxy materials (including a voting instruction card) are being forwarded to you by your broker, trustee, bank or nominee who is considered the shareholder of record with respect to those shares. As the beneficial owner, you have the right to direct your broker, trustee, bank or nominee on how to vote the shares in your account and are also invited to attend the Annual Meeting. However, since you are not the shareholder of record, you may not vote these shares during the Annual Meeting unless you request and obtain a proxy from your broker, trustee, bank or nominee. Your broker, trustee, bank or nominee has enclosed a voting instruction card for you to use in directing the broker, trustee, bank or nominee on how to vote your shares.

How do I vote?

Shareholders of Record. If you complete and properly sign the proxy card and return it to the Company, it will be voted as you direct. You may also vote via telephone or internet (as indicated on your proxy card). If you attend the virtual Annual Meeting, you may vote online during the Annual Meeting.

Beneficial Owners. If you complete and properly sign the voting instruction card and return it to your broker, trustee, bank or other nominee, it will be voted as you direct. You may also vote via telephone or internet (as indicated on your voting instruction card). If you want to vote your shares electronically during the Annual Meeting, you must request and obtain a proxy from such broker, trustee, bank or other nominee confirming that you beneficially own such shares and giving you the power to vote such shares.

Can I change my vote after I return my proxy card or voting instruction card?

Shareholders of Record. You may change your vote at any time before the proxy is exercised by filing with the Secretary of the Company, at 38505 Woodward Avenue, Suite 200, Bloomfield Hills, Michigan 48304, either written notice revoking the proxy or a properly signed proxy that is dated later than the proxy card. If you attend the Annual Meeting online, the individuals named as proxy holders in the proxy card will nevertheless have authority to vote your shares in accordance with your instructions on the proxy card unless you properly file such notice or new proxy.

Beneficial Owners. If you hold your shares through a bank, trustee, broker or other nominee, you should contact such person to submit new voting instructions prior to the time such voting instructions are exercised.

How will my shares be voted?

Shareholders of Record. All shares represented by the proxies mailed to shareholders will be voted electronically during the Annual Meeting in accordance with instructions given by the shareholders. Where no instructions are given, the shares will be voted (1) for the election of the Board’s nominees for two directors, (2) for the ratification of the appointment of Deloitte as the Company’s independent registered public accounting firm for the year ending December 31, 2025, and (3) for the approval, on a non-binding advisory basis, of the compensation paid to the Company’s NEOs.

Beneficial Owners. The brokers, banks or nominees holding shares for beneficial owners must vote those shares as instructed, and if no instructions from the beneficial owner are received on a matter deemed to be non-routine, they may not vote the shares on that matter. Under applicable law, a broker, bank or nominee has the discretion to vote on routine matters, such as Proposal 2, but does not have discretion to vote with respect to non-routine matters, such as Proposals 1 or 3. Common Stock subject to broker non-votes will be considered present at the meeting for purposes of determining whether there is a quorum. Broker non-votes will have no effect in determining the outcome of the vote on Proposal 1 and will have the effect of a vote against Proposal 3. In order to avoid a broker non-vote of your shares on this proposal, you must send voting instructions to your bank, broker or nominee.

What are the Board’s recommendations?

The Board recommends a vote:

Proposal 1 -FORthe election of the nominated slate of directors.

Proposal 2 -FORthe ratification of the appointment of Deloitte as the Company’s independent registered public accounting firm for the fiscal year ending December 31, 2025.

Proposal 3 -FORthe approval, on a non-binding advisory basis, of the compensation paid to the Company’s NEOs.

What vote is required to approve each item?

Proposal 1 - Election of Directors.

The two nominees who receive the most votes cast at the Annual Meeting will be elected as directors, provided a quorum of at least a majority of the outstanding shares of the Company’s Common Stock is represented at the meeting. However, we have adopted a majority voting policy that is applicable in uncontested director elections. This means that the plurality standard will determine whether a director nominee is elected, but our majority voting policy will further require that the number of votes cast “for” a director must exceed the number of votes “withheld” from that director or the director must submit his or her resignation. The Board, taking into account the recommendation of the Governance and Nominating Committee, would then determine whether to accept or reject any required resignation. A proxy card marked “Withhold All” or “For All Except” with respect to the election of one or more directors will not be voted with respect to the director or directors indicated. Abstentions and broker non-votes will each be counted as present for purposes of determining the presence of a quorum, but will have no effect on the election of directors.

Proposal 2 - Ratification of the Appointment of Independent Registered Public Accounting Firm.

The affirmative vote of a majority of the shares of Common Stock present or represented by proxy at the Annual Meeting will be necessary to ratify the Audit Committee’s appointment of Deloitte as the Company’s independent registered public accounting firm for the fiscal year ending December 31, 2025, provided that a quorum is present. Abstentions will have the same effect as a vote against the matter. Although shareholder ratification of the appointment is not required by law and is not binding on the Company, the Audit Committee will take the appointment under advisement if such appointment is not so ratified.

Proposal 3 - Approval, on a non-binding advisory basis, of the compensation paid to the Company’s NEOs.

The affirmative vote of a majority of the shares of Common Stock present or represented by proxy at the Annual Meeting will be necessary to approve the non-binding advisory resolution approving the compensation paid to the Company’s NEOs. While the Board intends to carefully consider the shareholder vote resulting from this proposal, the final vote is advisory in nature. Abstentions and broker non-votes will have the same effect as a vote against the matter.

What will happen if other matters are raised at the meeting?

If any other matter is properly submitted to the shareholders at the Annual Meeting, its adoption will require the affirmative vote of a majority of the shares of Common Stock outstanding on the Record Date that is present or represented at the Annual Meeting. The Board does not propose to conduct any business at the Annual Meeting other than as stated above.

How do I find out the voting results?

Preliminary voting results will be announced at the Annual Meeting and final voting results will be published by the Company in a Current Report on Form 8-K.

How may I obtain an additional copy of the proxy materials?

If you share an address with another shareholder, you may receive only one set of proxy materials unless you have provided contrary instructions. If you wish to receive a separate set of proxy materials now or in the future, please request the additional copy by contacting TriMas Corporation, Attention: Investor Relations, 38505 Woodward Avenue, Suite 200, Bloomfield Hills, Michigan 48304, Telephone 248-631-5450, or by email to generalcounsel@trimas.com. Additionally, if you have been receiving multiple sets of proxy materials and wish to receive only one set of proxy materials, please contact the Company’s Investor Relations department in the manner provided above.

What does it mean if I receive more than one proxy card or voting instruction card?

If you receive more than one proxy card or voting instruction card, it means that you have multiple accounts with banks, trustees, brokers, other nominees and/or the Company’s transfer agent. Please sign and deliver each proxy card and voting instruction card that you receive to ensure that all of your shares will be voted. We recommend that you contact your nominee and/or the Company’s transfer agent, as appropriate, to consolidate as many accounts as possible under the same name and address.

Who pays for the solicitation of proxies?

The accompanying proxy is being solicited by the Board. The Company will bear the cost of soliciting the proxies. Officers and other management employees of the Company will receive no additional compensation for the solicitation of proxies and may use mail, e-mail, personal interview and/or telephone.

How can I access the Company’s proxy materials and Annual Report on Form 10-K?

The Financial Information subsection under “Investors” on the Company’s website, www.trimas.com, provides access, free of charge, to SEC reports as soon as reasonably practicable after the Company electronically files such reports with, or furnishes such reports to, the SEC, including proxy materials, Annual Reports on Form 10-K, Quarterly Reports on Form 10-Q, Current Reports on Form 8-K and amendments to these reports. The Company has posted printable and searchable 2025 proxy materials to the Company’s website at http://ir.trimas.com. A copy of the Company’s Annual Report on Form 10-K for the year ended December 31, 2024, as filed with the SEC, will be sent to any shareholder, without charge, upon written request sent to the Company’s executive offices at TriMas Corporation, Attention: Investor Relations, 38505 Woodward Avenue, Suite 200, Bloomfield Hills, Michigan 48304, or by email to generalcounsel@trimas.com.

The references to the website address of the Company and SEC in this proxy statement are not intended to function as a hyperlink and, except as specified herein, the information contained on such websites is not part of this proxy statement.

Is a registered list of shareholders available?

The names of shareholders of record entitled to vote electronically at the Annual Meeting will be available to shareholders entitled to vote at the meeting on Wednesday, May 14, 2025, at the Company’s headquarters and during the meeting, atwww.virtualshareholdermeeting.com/TRS2025.

How and when may I submit a shareholder proposal or director nomination for the 2026 Annual Meeting?

For a shareholder proposal to be considered for inclusion in the Company’s proxy statement for the 2026 Annual Meeting, the Secretary must receive the written proposal at the Company’s principal executive offices no later than

November 27, 2025. Such proposals also must comply with SEC regulations under Rule 14a-8 regarding the inclusion of shareholder proposals in company-sponsored proxy materials. Proposals should be addressed to TriMas Corporation, General Counsel, 38505 Woodward Avenue, Suite 200, Bloomfield Hills, Michigan 48304, or by fax to (888) 318-8873.

For a shareholder proposal or director nomination that is intended to be considered at the 2026 Annual Meeting, but not included in the Company’s proxy statement, the shareholder must give timely notice to the Secretary not earlier than January 14, 2026, and not later than the close of business on February 13, 2026. Any shareholder proposal must set forth (1) a brief description of the business desired to be brought before the 2026 Annual Meeting and the reasons for conducting such business, (2) the name and address, as they appear on the Company’s books, of the shareholder proposing such business, (3) the number of shares of Common Stock that are beneficially owned by the shareholder, (4) any material interest of the shareholder in such business and (5) any additional information that is required to be provided by the shareholder pursuant to Regulation 14A under the Exchange Act or the Company’s Third Amended and Restated Bylaws.

In addition to satisfying the requirements under the Company’s Third Amended and Restated Bylaws, to comply with the universal proxy rules, shareholders who intend to solicit proxies in support of director nominees other than the Company’s nominees must provide notice that sets forth any additional information required by Rule 14a-19 under the Exchange Act, which notice must be postmarked or transmitted electronically to the Company at its principal executive offices no later than 60 calendar days prior to the first anniversary of this year’s Annual Meeting. If the date of the 2026 Annual Meeting is changed by more than 30 calendar days from the first anniversary of this year’s Annual Meeting, then notice must be provided by the later of 60 calendar days prior to the date of the 2026 Annual Meeting or the 10th calendar day following the day on which public announcement of the date of the 2026 Annual Meeting is first made. Accordingly, for the 2026 Annual Meeting, shareholders must deliver such notice no later than March 16, 2026.