January 28, 2021 Dear Shareholder: You are cordially invited to attend a special meeting of shareholders (as may be adjourned or postponed, the “special meeting”) of MTS Systems Corporation, a Minnesota corporation (which we refer to as the “Company”), which will be held virtually via the Internet on March 4, 2021 beginning at 11:00 AM Eastern Time. As part of our precautions regarding the COVID-19 (coronavirus) pandemic, we are sensitive to the public health and travel concerns that our shareholders may have, as well as any quarantines or other similar protocols that governments may impose. As a result, the special meeting will be held in a virtual meeting format only via live webcast. There will not be a physical meeting location. You or your proxyholder will be able to attend the special meeting online and vote your shares electronically by visiting www.virtualshareholdermeeting.com/MTSC2021SGM. Regardless of whether you plan to attend the special meeting, we encourage you to vote your shares now by mail, by telephone or through the Internet by following the procedures outlined below. The purpose of the special meeting is to consider and vote on proposals relating to the proposed acquisition of the Company by Amphenol Corporation, a Delaware corporation (which we refer to as “Parent”). On December 8, 2020, the Company, Parent and Moon Merger Sub Corporation, a Minnesota corporation and a wholly-owned subsidiary of Parent (which we refer to as “Sub”), entered into an Agreement and Plan of Merger (as may be amended from time to time and including the plan of merger attached as Exhibit A thereto, the “merger agreement”). The merger agreement provides for, subject to the satisfaction or waiver of specified conditions, the acquisition of the Company by Parent at a price of $58.50 per share in cash, without interest thereon, subject to any applicable withholding taxes. Subject to the terms and conditions of the merger agreement, Sub will be merged with and into the Company (which we refer to as the “merger”), with the Company continuing as the surviving corporation in the merger. As a result of the merger, the Company will become a wholly-owned subsidiary of Parent. The proxy statement accompanying this letter provides you with more specific information concerning the special meeting, the merger agreement, the merger and the other transactions contemplated by the merger agreement. We encourage you to carefully read the accompanying proxy statement and the copy of the merger agreement attached as Annex A to the proxy statement. At the effective time of the merger (which we refer to as the “effective time”), each share of common stock of the Company, par value $0.25 per share (which we refer to as “Company common stock”) issued and outstanding immediately prior to the effective time will be cancelled and cease to exist and will be automatically converted into the right to receive $58.50 in cash, without interest thereon, other than (i) shares that are owned of record by any subsidiary of the Company (other than those held on behalf of a third party), (ii) shares owned of record by Parent, Sub or any of their respective subsidiaries (other than those held on behalf of a third party) and (iii) shares held by shareholders who have not voted in favor of approval and adoption of the merger agreement and who are entitled to demand and properly exercise dissenters’ rights with respect to such shares and complied in all respects with all the applicable provisions of the Minnesota Business Corporation Act. The board of directors of the Company (which we refer to as the “Board”) carefully reviewed and considered the terms and conditions of the merger agreement, the merger and the other transactions contemplated by the merger agreement. The Board has (i) determined that the merger agreement and the transactions contemplated thereby are in the best interests of the Company and its shareholders, (ii) unanimously approved, adopted and declared advisable the execution, delivery and performance of the merger agreement by the Company, and, subject to receiving the Company shareholder approval, the consummation by the Company of the transactions contemplated by the merger agreement, including the merger, (iii) directed that the approval and adoption of the merger agreement be submitted to a vote of the shareholders of the Company at a shareholder meeting called for such purpose and (iv) resolved to recommend approval and adoption of the merger agreement by the shareholders of the Company in accordance with applicable provisions of the laws of the State of Minnesota at such shareholder meeting on the terms set forth in the merger agreement. Accordingly, the Board unanimously recommends a vote “FOR” the proposal to approve and adopt the merger agreement and the other proposals set forth in the accompanying proxy statement. Your vote is important. Whether or not you plan to attend the special meeting and regardless of the number of shares you own, your careful consideration of, and vote on, the proposal to approve and adopt the merger agreement is important, and we encourage you to vote promptly. The merger cannot be completed unless the merger agreement is approved and adopted by shareholders holding at least a majority of the outstanding voting shares of Company common stock. The failure to vote will have the same effect as a vote “AGAINST” the proposal to approve and adopt the merger agreement. After reading the accompanying proxy statement, please make sure to vote your shares promptly by completing, signing and dating the accompanying proxy card and returning it in the enclosed prepaid envelope or by voting by telephone or through the Internet. Instructions regarding all three methods of voting are provided on the proxy card. If you hold shares through an account with a bank, broker, trust or other nominee, please follow the instructions you receive from it to vote your shares. Thank you in advance for your continued support and your consideration of this matter. Sincerely, David J. Anderson Randy J. Martinez Chairman of the Board President and Chief Executive Officer Neither the United States Securities and Exchange Commission nor any state securities regulatory agency has approved or disapproved the merger, passed upon the merits or fairness of the merger or passed upon the adequacy or accuracy of the disclosure in this document. Any representation to the contrary is a criminal offense. The accompanying notice of special meeting and proxy statement are being mailed to Company shareholders on or about January 29, 2021. MTS Systems Corporation 14000 Technology Drive Eden Prairie, Minnesota 55344 NOTICE OF SPECIAL MEETING OF SHAREHOLDERS To Be Held on March 4, 2021 To the Shareholders of MTS Systems Corporation: A special meeting of the shareholders (as may be postponed or adjourned, which we refer to as the “special meeting”) of MTS Systems Corporation (which we refer to as the “Company”) will be held virtually via the Internet on March 4, 2021 beginning at 11:00 AM Eastern Time. As part of our precautions regarding the COVID-19 (coronavirus) pandemic, we are sensitive to the public health and travel concerns that our shareholders may have, as well as any quarantines or other similar protocols that governments may impose. As a result, the special meeting will be held in a virtual meeting format only via live webcast. There will not be a physical meeting location. You or your proxyholder will be able to attend the special meeting online and vote your shares electronically by visiting www.virtualshareholdermeeting.com/MTSC2021SGM (which we refer to as the “special meeting website”). The special meeting will be held to consider and vote on proposals to: 1. approve and adopt the Agreement and Plan of Merger, dated as of December 8, 2020 (as may be amended from time to time and including the plan of merger attached as Exhibit A thereto, the “merger agreement”), by and among the Company, Amphenol Corporation, a Delaware corporation (which we refer to as “Parent”) and Moon Merger Sub Corporation, a Minnesota corporation and a wholly-owned subsidiary of Parent (which we refer to as “Sub”); 2. consider and vote on a proposal to approve, by a non-binding advisory vote, the compensation that may be paid or become payable to the Company’s named executive officers and that is based on, or otherwise relates to, the merger of Sub with and into the Company (which we refer to as the “merger”), as contemplated by the merger agreement; and 3. consider and vote on a proposal to adjourn the special meeting from time to time to a later date or time if necessary or appropriate, including to solicit additional proxies in favor of the proposal to approve and adopt the merger agreement if there are insufficient votes at the time of the special meeting to approve and adopt the merger agreement. Shareholders of record at the close of business on January 27, 2021 are entitled to notice of, and to vote at, the special meeting. For more information concerning the special meeting, the merger agreement, the merger and the other transactions contemplated by the merger agreement, please review the accompanying proxy statement and the copy of the merger agreement attached as Annex A to the proxy statement. The board of directors of the Company (which we refer to as the “Board”) carefully reviewed and considered the terms and conditions of the merger agreement, the merger and the other transactions contemplated by the merger agreement. The Board has (i) determined that the