AMENDMENT NO. 4 TO RIGHTS AGREEMENT

THIS AMENDMENT NO. 4 TO RIGHTS AGREEMENT (this “Amendment”), dated as of
October 2, 2007, is between Milacron Inc., a Delaware corporation (the
“Company”), and Mellon Investor Services LLC (formerly known as ChaseMellon
Shareholder Services, L.L.C.), a New Jersey limited liability company, as rights
agent (the “Rights Agent”).

WHEREAS, the Company and the Rights Agent are parties to a Rights Agreement
dated as of February 5, 1999, as amended by Amendment No. 1 thereto dated as of
March 11, 2004, Amendment No. 2 thereto dated as of June 9, 2004, and by
Amendment No. 3 thereto dated as of October 1, 2007, between the Company and the
Rights Agent (the “Rights Agreement”); and

WHEREAS, pursuant to Section 26 of the Rights Agreement, the Company and the
Rights Agent desire to further amend the Rights Agreement as set forth below;

NOW, THEREFORE, the Rights Agreement is hereby amended as follows:

  1.   Amendment of Section 1.

Section 1 of the Rights Agreement is hereby amended to add the following new
definition:

“Securities Purchase Agreement” shall mean the Securities Purchase Agreement to
be entered into on or about October 2, 2007, by and among Ohio Plastics, LLC and
Glencore Finance AG.

  2.   Addition of new Section 35.

The Rights Agreement is amended by adding thereto a new Section 35 thereof to
read in its entirety as follows:

“Section 35. Exception for Securities Purchase Agreement. Notwithstanding any
provision of the Rights Agreement to the contrary, a Distribution Date shall not
be deemed to have occurred, none of the transactions, events or rights under
Section 11 of this Rights Agreement shall become applicable or be triggered,
none of Ohio Plastics, LLC or any of its Affiliates or Associates shall be
constituted or deemed to be or have become an Acquiring Person, and no holder of
any Rights shall be entitled to exercise such Rights under or be entitled to any
rights pursuant to this Agreement, including, without limitation, to any of
Sections 3, 7 or 11 of this Rights Agreement, in all such cases by reason or as
a consequence of the approval, execution, delivery, announcement, pendency of,
or consummation of any of the transactions contemplated by, the Securities
Purchase Agreement.”

  3.   Compliance.

By its execution and delivery hereof, the Company states that this Amendment is
in compliance with the terms of Section 26 of the Rights Agreement and directs
the Rights Agent to execute this Amendment.

  4.   Effectiveness.

This Amendment shall be effective upon its execution by both parties hereto.
Except as expressly amended hereby, this Rights Agreement shall remain in full
force and effect and shall otherwise be unaffected hereby. Upon the
effectiveness of this Amendment, the term “Rights Agreement” as used in the
Rights Agreement shall refer to this Rights Agreement as amended hereby.

  5.   Miscellaneous.

This Amendment No. 4 shall be deemed to be a contract made under the laws of the
State of Delaware and for all purposes shall be governed by and construed in
accordance with the laws of such state applicable to contracts to be made and
performed entirely within such state. This Amendment may be executed in
counterparts, each of such counterparts shall for all purposes be deemed to be
an original, and all such counterparts together shall constitute but one and the
same instrument. If any term, provision, covenant or restriction of this
Amendment is held by a court of competent jurisdiction or other public or
governmental authority to be invalid, illegal, or unenforceable, the remainder
of the terms, provisions, covenants and restrictions of this Amendment shall
remain in full force and effect and shall in no way be affected, impaired or
invalidated.

[Signature Page Follows]

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IN WITNESS WHEREOF, the parties hereto have caused this Amendment No. 4 to be
duly executed and delivered as of the date first set forth above.

MILACRON INC.

     
By:
  /s/ Hugh C. O’Donnell
Name: Hugh C. O’Donnell
Title: Senior Vice President, General
Counsel and Secretary

    MELLON INVESTOR SERVICES LLC,

as Rights Agent

     
By:
  /s/ Mitzi Brinkman
Name: Mitzie Brinkman
Title: Relationship Manager

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