SECURITIES AND EXCHANGE COMMISSION

WASHINGTON, D.C. 20549

SCHEDULE TO

(Rule 14d-100)

TENDER OFFER STATEMENT PURSUANT TO SECTION 14(d)(1) OR 13(e)(1)

OF THE SECURITIES EXCHANGE ACT OF 1934

(Amendment No. 6—Final Amendment)^*

and

SCHEDULE 13D

(Amendment No. 1)

(Rule 13d-101)

Under the Securities Exchange Act of 1934

Denison International plc

(Name of Subject Company (Issuer))

Parker-Hannifin Corporation

(Name of Filing Persons (Offeror))

Ordinary Shares, $0.01 par value per share, and

American Depositary Shares each representing one Ordinary Share

(Title of Class of Securities)

248335101

(CUSIP Number of Class of Securities)

Thomas A. Piraino, Jr.

Vice President, General Counsel and Secretary

Parker-Hannifin Corporation

6035 Parkland Boulevard

Cleveland, Ohio 44124-4141

(216) 896-3000

(Name, Address and Telephone Numbers of Person Authorized to Receive Notices and Communications on Behalf of Filing Persons)

Copy to:

Patrick J. Leddy

Jones Day

North Point

901 Lakeside Avenue

Cleveland, Ohio 44114-1190

(216) 586-3939

February 12, 2004

(Date of Event Which Requires Filing of this Statement)

CALCULATION OF FILING FEE

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*SEE INSTRUCTIONS BEFORE FILLING OUT!

This Amendment No. 6 amends and supplements the Tender Offer Statement on Schedule TO filed with the Securities and Exchange Commission on December 19, 2003, as amended by Amendment No. 1 filed with the Securities and Exchange Commission on December 31, 2003, Amendment No. 2 filed with the Securities, Exchange Commission on January 13, 2004, Amendment No. 3 filed with the Securities and Exchange Commission on January 22, 2004, Amendment No. 4 filed with the Securities and Exchange Commission on February 5, 2004 and Amendment No. 5 filed with the Securities and Exchange Commission on February 10, 2004 (as amended, the “Schedule TO”), by Parker-Hannifin Corporation, an Ohio corporation (“Parker”). The Schedule TO relates to the offer by Parker to purchase all of the Ordinary Shares, $0.01 par value per share (the “Ordinary Shares”) outstanding at any time during the Offer (as defined herein), including those Ordinary Shares represented by American Depositary Shares each representing one Ordinary Share, of Denison International plc (“Denison”) at a purchase price of $24.00 per Ordinary Share, net to the seller in cash, without interest thereon, upon the terms and subject to the conditions set forth in the Offer To Purchase, dated December 19, 2003 (the “Offer To Purchase”), and in the related Letter of Transmittal and Form of Acceptance (as they may be amended or supplemented from time to time, together constitute the “Offer”), a copy of each of which was filed with the Schedule TO on December 19, 2003 as Exhibits (a)(1)(A), (a)(1)(B) and (a)(1)(C), respectively. In addition, Parker offered to purchase all of the outstanding A Ordinary Shares, £8.00 par value per share, of Denison, which class of securities is not registered under the Securities Exchange Act of 1934, at a purchase price of $24.00 per share, net to the seller in cash, without interest thereon, upon the terms and subject to the conditions of the Offer. This Amendment No. 6 to the Schedule TO is being filed on behalf of Parker.

Item 6 of the Schedule TO is hereby amended and supplemented by adding thereto the following:

“Parker intends to exercise its rights pursuant to Sections 428 to 430F of the UK Companies Act 1985 to compulsorily acquire all A Ordinary Shares and Ordinary Shares that it did not acquire pursuant to the Offer. A copy of each of the form of letter to non-assenting holders of A Ordinary Shares, form of letter to non-assenting holders of Ordinary Shares, form of Section 429(4) notice to non-assenting holders of A Ordinary Shares and Ordinary Shares, form of Section 429dec notice of compulsory acquisition and form of the advertisement to be placed in the London Gazette are filed as Exhibits (a)(5)(G), (a)(5)(H), (a)(5)(I), (a)(5)(J) and (a)(5)(K), respectively, to the Schedule TO and are hereby incorporated herein by reference.”

Item 8 of the Schedule TO is hereby amended and supplemented by adding thereto the following:

“The Offer expired at 8:00 a.m., New York City time, on Thursday, February 12, 2004. Based on information provided by the Depositary, as of the expiration of the Offer, approximately 6,973 A Ordinary Shares, or approximately 99% of the outstanding A Ordinary Shares on a fully diluted basis, and approximately 10,163,704 Ordinary Shares, including those Ordinary Shares represented by ADSs of which 2,600 were tendered pursuant to guaranteed delivery procedures, in total representing 96% of the outstanding Ordinary Shares on a fully diluted basis, were validly tendered and not withdrawn. Parker has accepted for payment, and notified the Depositary to promptly pay for, the tendered and accepted Shares in accordance with the terms and conditions of the Offer.

On February 12, 2004, Parker and Denison issued a joint press release announcing the completion of the Offer. A copy of the press release issued by Parker and Denison on February 12, 2004 is filed herewith as Exhibit (a)(5)(F) and is incorporated herein by reference.”

Item 12 of the Schedule TO is hereby amended and supplemented by adding thereto the following:

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SIGNATURE

After due inquiry and to the best of my knowledge and belief, I certify that the information set forth in this statement is true, complete and correct.

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Exhibit Index

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