Document:

<PAGE>
                                                                     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."

                  (c) Schedule 2 (Commitments of Lenders) to the Loan Agreement
is amended and restated in the form of Annex I hereto.

         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:

<PAGE>

                  (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,

                                      -2-
<PAGE>

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.

                                      -3-
<PAGE>

                  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

                                      -4-
<PAGE>

                                      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

                                      By: /s/ AUTHORIZED SIGNATORY
                                         ---------------------------------------
                                         Name:
                                         Title:

                                      BANK OF AMERICA, N.A.

                                      By: /s/ AUTHORIZED SIGNATORY
                                         ---------------------------------------
                                         Louis M. Alexander
                                         Senior Vice President

                                      JP MORGAN CHASE BANK

                                      By: /s/ AUTHORIZED SIGNATORY
                                         ---------------------------------------
                                         Name:
                                         Title:

                                      -5-
<PAGE>

                                      FLEET CAPITAL CORPORATION

                                      By: /s/ AUTHORIZED SIGNATORY
                                         ---------------------------------------
                                         Name:
                                         Title:

                                      LASALLE BUSINESS CREDIT, INC.

                                      By: /s/ AUTHORIZED SIGNATORY
                                         ---------------------------------------
                                         Name:
                                         Title:

                                      CDN. LENDER

                                      TRANSAMERICA COMMERCIAL
                                      FINANCE CORPORATION, CANADA

                                      By: Transamerica Business Capital
                                      Corporation, as Attorney-in-Fact

                                      By: /s/ AUTHORIZED SIGNATORY
                                         ---------------------------------------
                                         Name:
                                         Title:

                                      AGENT

                                      TRANSAMERICA BUSINESS CAPITAL
                                      CORPORATION

                                      By: /s/ AUTHORIZED SIGNATORY
                                         ---------------------------------------
                                         Name:
                                         Title:

                                      -6-
<PAGE>

                                      CDN. AGENT

                                      TRANSAMERICA COMMERCIAL
                                      FINANCE CORPORATION, CANADA

                                      By: Transamerica Business Capital
                                      Corporation, as Attorney-in-Fact

                                      By: /s/ AUTHORIZED SIGNATORY
                                         ---------------------------------------
                                         Name:
                                         Title:

                                      -7-
<PAGE>

ACKNOWLEDGED AND AGREED AS OF
THE DATE FIRST SET FORTH ABOVE:

GRANT PRIDECO, INC.

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

GRANT PRIDECO USA, LLC

By: /s/ DAVE WEIGEL
   ---------------------------------
   Name:  Dave Weigel
   Title: President

XL SYSTEMS INTERNATIONAL, INC.

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

TA INDUSTRIES, INC.

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

GRANT PRIDECO HOLDING, LLC

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

GP EXPATRIATE SERVICES, INC.

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

                                      -8-
<PAGE>

TUBE-ALLOY CAPITAL CORPORATION

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

INTELLIPIPE, INC.

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

GRANT PRIDECO PC COMPOSITES HOLDINGS, LLC

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

PLEXUS DEEPWATER TECHNOLOGIES, LTD.

By: Grant Prideco Holding, LLC,
its general partner

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

                                      -9-
<PAGE>

                                                                       EXHIBIT A

                               [Form of TBCC Note]

<PAGE>

                                                                       EXHIBIT B

                  [Form of LaSalle Business Credit, Inc. Note]

<PAGE>

                                                                         ANNEX I

                                                                      SCHEDULE 2

                             COMMITMENTS OF LENDERS

<Table>
<Caption>
                                                                                                   Cdn. Loan and Cdn.
                                                               U.S. Loan and U.S. Letter            Letter of Credit
                        Lenders                                   of Credit Commitment                Commitment
--------------------------------------------------------- ---------------------------------- -------------------------------
<S>                                                       <C>                                <C>
Transamerica Business Capital Corporation                           US$35,000,000                         -0-
Address:
555 Theodore Fremd Avenue
Suite C-301
Rye, New York  10580
Telecopier: (914) 921-0110
Attn.: Mr. Steven R. Fischer

Bank of America, N.A.                                               US$35,000,000                         -0-
Address:
40 East 52nd Street
New York, New York  10022
Telecopier: (212) 836-5169
Attn.: Mr. Louis Alexander

JP Morgan Chase Bank                                                US$25,000,000                         -0-
Address:
2200 Ross Avenue, 4th floor
Dallas, Texas  75201
Telecopier: (214) 965-4731
Attn.: Mr. Chad Ramsey

Fleet Capital Corporation                                            US$25,000,000                        -0-
5950 Sherry Lane, Suite 300
Dallas, TX  75225
Telecopier: (214) 706-7066
Attn.: Loan Administration Manager

LaSalle Business Credit, Inc.                                        US$15,000,000                        -0-
565 Fifth Avenue
27th Floor
New York, New York 10017
Telecopier: (212) 986-4205
Attn.: Mr. A. Roger Craig
</Table>

<PAGE>

<Table>
<S>                                                       <C>                                <C>
Transamerica Commercial Finance Corporation, Canada                      -0-                         US$7,000,000(1)
Address:201 City Centre Drive,                                                                   (or Equivalent Amount)
Suite 500
Mississauga, Ontario
CANADA L5B 2T4
Telecopier: (905) 273-7864
Attn.: Mr. Peter D. Kelley
</Table>

--------
(1) The Cdn. Commitments are a sublimit of the U.S. Commitments.

                                      -2-<PAGE>
                                                                   EXHIBIT 10.10

November 9, 2000

Mr. Marshall Danby
318 Bayshore Drive
Montgomery, Texas 77356

Dear Marshall:

We are pleased to offer you the position of Vice President and General Manager
of the Drill Tube International division of Grant Prideco L. P., effective on or
about December 1, 2000 (the "Start Date") with the following terms and
conditions.

POSITION

1.       Title, Grade and Reporting
         Your title will be Vice President and General Manager Drill Tube
         International, (Grant Prideco Salary Grade 23) and you will report to
         John Coble, President Grant Prideco, L. P. ("Grant Prideco"). As you
         are aware, you also will be working very closely with Steve Turner, the
         current President of our Drill Tube division. Working with Steve to
         achieve a smooth transition is very important.

2.       Job Duties
         Your job duties will be outlined by John Coble.

COMPENSATION AND BENEFITS

1.       Base Salary and Auto Allowance

         Your salary will be paid at the bi-weekly rate of $5,769.23, ("Base
         Salary"). Your next scheduled salary review will be January 1, 2002. In
         addition, you will also be eligible for an auto allowance of $600 per
         month, plus reimbursement of business mileage according to Company
         policy.

2.       Hiring Bonus

         You will be eligible for a hiring bonus of $25,000 to be paid within
         thirty (30) days of your start date at Grant Prideco.

<PAGE>

3.       Severance Agreement

         If your employment is terminated for any reason other than "for cause"
         during the first twenty-four (24) months of your start date, you will
         be eligible for a severance payment equal to one (1) year of your then
         current base pay. Your Severance Agreement will automatically expire at
         the end of the twenty-four (24) months from the Start Date. For the
         purpose of this paragraph, term " for cause" includes, but is not
         limited to, any one or more of the following occurrences: (a) your
         breach of any of any representations contained herein; (b) your
         conviction by, or enter of a plea of guilty or nolo contrendre for any
         crime (excluding traffic violations and similar misdemeanors) involving
         moral turpitude or which is punishable by imprisonment; (c) your
         commission of an act of fraud, whether prior or subsequent to the date
         hereof, upon Grant Prideco or any of its customers or affiliates; (d)
         your failure or refusal to perform his duties as required hereunder by
         this Agreement, (e) Gross negligence in performance of your duties,
         theft of the Grant Prideco's property, material violation of any duty
         of loyalty to Grant Prideco or any other material misconduct; or (f)
         Material violation of Grant Prideco's Employee Policy in effect at that
         time, including without limitation, the receipt or payment of any
         kick-back or side payment from or to any customer, supplier or vendor,
         or government.

4.       Management Incentive Program

         In addition to your base salary, you will be eligible for the
         discretionary Management Incentive Program, which will be outlined by
         John Coble. This program is designed to pay a cash incentive based on
         the attainment of pre-determined performance objectives. Management
         reserves the right to change the provisions of this program at any
         time, however, at present, your position would be eligible for a bonus
         payment of 40%/ 80%/120% (minimum/target/maximum) of your base salary
         if the objectives are achieved.

5.       Executive Deferred Compensation Plan (EDC)

         You will be eligible to participate in Grant Prideco's EDC program that
         will provide you with opportunities to both purchase and receive,
         through grants, Grant Prideco stock based upon a percentage
         contribution of your eligible cash compensation. At a minimum, Grant
         Prideco will contribute on your behalf 7 1/2% of your eligible total
         annual compensation to the plan. At your option, you may contribute up
         to 7 1/2% of your compensation and Grant Prideco will match up to 7
         1/2% on a dollar for dollar basis. The maximum amount deferred is 22
         1/2%. Vesting will take place at 20% per year over a five-year period.
         Grant Prideco stock will be acquired at then prevailing current market
         prices. A synopsis of the plan is enclosed for your review.

<PAGE>

6.       Stock Option

         You will be offered 100,000 options for Grant Prideco stock with
         three-year cliff vesting (vesting on the third anniversary of your date
         of employment) with an option price at the prevailing market rate.

7.       Benefits

         You will be eligible to participate in the Grant Prideco's medical,
         dental, vision, life and disability plans on the first day of the month
         after you complete thirty (30) days of active employment. You will also
         be eligible to participate in Grant Prideco's 401(k) plan after six (6)
         months of active employment.

8.       Vacation/Holidays

         You will be entitled to ten (10) Grant Prideco designated holidays and
         your vacation benefits will accrue at the rate of three (3) weeks
         vacation per year.

EMPLOYEE REPRESENTATIONS

1.       No Conflicts In accepting these terms of employment you represent and
         warrant that you are under no contractual or other obligation, which
         would, in any way, limit, restrict or prevent your ability to perform
         your duties hereunder.

2.       No Confidential Information You acknowledge that Grant Prideco has
         informed you that, in connection with the performance of your duties
         for Grant Prideco, you shall in no way use, disclose, or rely upon any
         trade secret or other confidential information you may possess (if any)
         by virtue of his experience in the industry (including, but not limited
         to, trade secret or confidential information of your previous
         employer).

MISCELLANEOUS

1.       Identity and Employment Eligibility

         Within three (3) business days of employment, you will need to provide
         a document or documents that establish identity and employment
         eligibility. This offer is contingent on certification of these
         documents.

2.       Drug Screening/Physical Examination

         Prior to commencement of employment, and as a condition of employment
         with Grant Prideco, you will be required to obtain a complete physical
         examination and submit a urine specimen for drug screening. Your
         employment with Grant Prideco, is contingent upon a negative drug
         screen result. Upon your acceptance of this offer, you will be provided
         with complete details for specimen collection and completion of
         physical. Upon acceptance, please contact Alicia Roye at (713) 466-8160
         to schedule a convenient time and location for this examination.

<PAGE>

3.       Patent and Confidential Information Agreement

         In accordance with Grant Prideco's Policy on Conflicts of Interest and
         Confidential Information, you will be required to sign an Agreement
         addressing these issues. A copy of this agreement is attached for your
         review.

4.       Non-Compete

         During the initial two year period of your employment following your
         start date, you agree that you will not compete against Grant Prideco
         in any capacity anywhere in North America (unless your employment is
         terminated by Grant Prideco without `cause').

This offer will remain in effect for two weeks after the date of the letter
unless the date is extended by mutual agreement. If you have any questions
regarding these items, please contact me at your earliest convenience.

Please indicate your acceptance of this agreement by signing and returning one
copy to the Human Resources Department.

     /s/ MARSHALL DENBY
------------------------------------        -----------------
Acceptance Signature                        Date

Sincerely,

/s/ WARREN AVERY
Warren Avery
Vice President Human Resources

cc:      John Coble, President

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