EXHIBIT 4.6

FIFTH AMENDMENT
TO LOAN AND SECURITY AGREEMENT

THIS FIFTH AMENDMENT dated as of January 25, 2002 (this "Amendment") to
the Amended and Restated Loan and Security Agreement, dated as of July 10, 2000
(the "Loan Agreement"; capitalized terms defined therein shall have the same
meanings when used herein unless otherwise defined herein), among each of the
direct and indirect Subsidiaries of Grant Prideco, Inc. ("GPI") specified on
Schedule 1 thereto (the "Borrowers"), the financial institutions from time to
time party thereto as lenders (the "Lenders"), Transamerica Business Capital
Corporation ("TBCC"), as agent for the U.S. Lenders (the "Agent"), and
Transamerica Commercial Finance Corporation, Canada, as agent for the Cdn.
Lenders (together with the Agent, the "Agents").

WITNESSETH:

WHEREAS, the Borrowers, the Lenders and the Agents are parties to the
Loan Agreement, under which the U.S. Borrowers may, subject to the terms
thereof, borrow U.S. Loans of up to US$125,000, 000;

WHEREAS, the Borrowers have requested that the Agents and the Lenders
amend the Loan Agreement to increase the maximum amount of U.S. Loans that the
U.S. Borrowers may borrow to US$135,000,000; and

WHEREAS, the parties hereto wish to amend the Loan Agreement to include
LaSalle Business Credit, Inc. as a U.S. Lender.

NOW, THEREFORE, the Borrowers, the Lenders and the Agents agree as
follows:

SECTION 1. AMENDMENTS TO THE LOAN AGREEMENT. Effective as of the date
hereof, but subject to the satisfaction of the conditions to effectiveness set
forth in Section 2 hereof, the Loan Agreement is amended as follows:

(a) Section 2.4(a)(ii) of the Loan Agreement is amended by
deleting "US$125,000,000" and substituting therefor "US$135,000,000."

(b) Section 4.4(a)(i) of the Loan Agreement is amended by
deleting "US$125,000,000" and substituting therefor "US$135,000,000."

SECTION 2. CONDITIONS TO EFFECTIVENESS. This Amendment shall not be
effective unless and until each of the following conditions shall have been
satisfied, in the Agent's reasonable determination, on or before January 25,
2002:

(a) The Agent shall have received the following, each dated
the date of delivery thereof or as of an earlier date acceptable to the Agent,
in form and substance acceptable to the Agent:

(i) a counterpart of this Amendment, duly executed by each
Borrower and acknowledged by each Guarantor;

(ii) an amended and restated promissory note payable to the
order of TBCC in the maximum principal amount of US$35,000,000,
substantially in the form of Exhibit A, duly executed by each U.S.
Borrower;

(iii) a promissory note payable to the order of LaSalle
Business Credit, Inc. in the maximum principal amount of US$15,000,000,
substantially in the form of Exhibit B, duly executed by each U.S.
Borrower;

(iv) a copy of the resolutions of the Board of Directors (or
similar evidence of authorization) of each Loan Party authorizing the
execution, delivery and performance of this Amendment and the
transactions contemplated hereby, attached to which is a certificate of
the Secretary or an Assistant Secretary of such Loan Party certifying
(A) that such copy of the resolutions (or similar evidence of
authorization) of such Loan Party is a true, complete and accurate copy
thereof and that such resolutions have not been amended or modified
since the date of such certificate and are in full force and effect and
(B) the incumbency, names and true signatures of the officers of such
Loan Party authorized to sign this Amendment; and

(v) such other agreements, instruments, documents and evidence
as the Agent deems necessary in its sole and absolute discretion in
connection with the transactions contemplated hereby; and

(b) the Borrowers shall have reimbursed the Agent for all
fees, costs and expenses (including, without limitation, the fees and expenses
of Luskin, Stern & Eisler LLP) incurred by the Agent in connection with the
preparation, negotiation, approval, execution and delivery of this Amendment.

SECTION 3. REFERENCE TO AND EFFECT ON THE LOAN DOCUMENTS.

(a) On and after the date hereof, each reference in the Loan
Agreement to "this Agreement," "hereunder," "hereof," "herein" and words of like
import, and each reference in the other Loan Documents to the Loan Agreement
shall mean and be a reference to the Loan Agreement as amended hereby.

(b) Except as specifically amended above, the Loan Agreement
shall remain in full force and effect and is hereby ratified and confirmed.

(c) The execution, delivery and effectiveness of this
Amendment shall not, except as expressly provided herein, operate as a waiver of
or an amendment to any right,

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power or remedy of the Agent or any Lender under any of the Loan Documents, or
constitute a waiver of or an amendment to any provision of any of the Loan
Documents.

(d) This Amendment shall constitute a Loan Document.

(e) Subject to the satisfaction of the conditions to
effectiveness set forth in Section 2, on and after the date hereof, (i) the U.S.
Lenders shall be deemed to include LaSalle Business Credit, Inc. and (ii)
LaSalle Business Credit, Inc. shall be a party to the Loan Agreement and, to the
extent provided in the Loan Agreement, this Amendment and the other Loan
Documents, have the rights and obligations of a U.S. Lender thereunder.

SECTION 4. COUNTERPARTS; TELECOPIED SIGNATURES. This Amendment may be
executed in counterparts and by the parties hereto in separate counterparts,
each of which when so executed and delivered shall be an original, but all of
which shall together shall constitute one and the same instrument. This
Amendment may be executed and delivered by telecopier or other facsimile
transmission all with the same force and effect as if the same was a fully
executed and delivered original, manual counterpart.

SECTION 5. GOVERNING LAW. This Amendment shall be governed by, and
construed in accordance with, the internal laws (as opposed to the conflicts of
law provisions other than section 5-1401 of the New York General Obligations
Law) and decisions of the State of New York.

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IN WITNESS WHEREOF, each of the parties hereto has caused this
Amendment to be executed by its (or its general partner's or managing member's)
proper and duly authorized officer as of the date first set forth above.

U.S. BORROWERS

GRANT PRIDECO, LP

By: Grant Prideco Holding, LLC,
its general partner

By: /s/ PHILIP A. CHOYCE
---------------------------------------
Philip A. Choyce
Vice President

XL SYSTEMS, L.P.

By: Grant Prideco Holding, LLC,
its general partner

By: /s/ PHILIP A. CHOYCE
---------------------------------------
Philip A. Choyce
Vice President

TEXAS ARAI, INC.

By: /s/ PHILIP A. CHOYCE
---------------------------------------
Philip A. Choyce
Vice President

TUBE-ALLOY CORPORATION

By: /s/ PHILIP A. CHOYCE
---------------------------------------
Philip A. Choyce
Vice President

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STAR OPERATING COMPANY

By: /s/ PHILIP A. CHOYCE
---------------------------------------
Philip A. Choyce
Vice President

CDN. BORROWER

GRANT PRIDECO CANADA LTD.

By: /s/ PHILIP A. CHOYCE
---------------------------------------
Philip A. Choyce
Secretary

U.S. LENDERS

TRANSAMERICA BUSINESS CAPITAL
CORPORATION