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                                                                     Exhibit 4.1

          THIS SUBORDINATED PROMISSORY NOTE IS SUBORDINATED TO THE OBLIGATIONS
OF THE MAKER UNDER THE GUARANTY OF EVEN DATE HEREWITH BY THE MAKER IN FAVOR OF
TRANSAMERICA BUSINESS CREDIT CORPORATION, AS AGENT ("AGENT"), IN THE MANNER AND
TO THE EXTENT SET FORTH IN THE SUBORDINATION AGREEMENT AMONG PAYEE, AGENT,
MAKER AND CERTAIN SUBSIDIARIES OF MAKER.


                          SUBORDINATED PROMISSORY NOTE


$100,000,000                   Houston, Texas                     April 14, 2000


         1.       FOR VALUE RECEIVED, the undersigned, GRANT PRIDECO, INC., a
Delaware corporation ("Maker"), hereby promises to pay to the order of
WEATHERFORD INTERNATIONAL, INC., a Delaware corporation (the "Payee"), in
Houston, Harris County, Texas, at 515 Post Oak Blvd., Suite 600, on or before
March 31, 2002 (the "Maturity Date"), in lawful money of the United States of
America, the principal amount of ONE HUNDRED MILLION DOLLARS, together with
interest on the unpaid balance of said principal amount from time to time
remaining outstanding, from the date hereof until maturity (howsoever such
maturity shall occur), in like money, at said office, at a rate per annum equal
to the lesser of (a) the Note Rate and (b) the Maximum Rate.

         2.       All past due principal of and interest on this Note shall bear
interest from the due date thereof (whether by acceleration or otherwise) until
paid at a per annum rate equal to the lesser of (a) the Note Rate plus 2% and
(b) the Maximum Rate.

         3.       Accrued unpaid interest on the outstanding principal balance
hereof shall be due and payable by Maker to Payee on the last Business Day of
each March, June, September and December, commencing June 30, 2000. The
outstanding principal balance of this Note shall be due and payable on the
Maturity Date; provided that all unpaid accrued interest on this Note, and the
outstanding unpaid principal balance hereof, shall be immediately due and
payable in full upon the maturity of the principal of this Note, whether by
acceleration or otherwise. All principal and interest payments under this Note
shall be subject to the provisions of the Subordination Agreement.

         4.       Maker shall have the right and privilege of prepaying this
Note, in whole or in part, at any time or from time to time without premium or
penalty or notice to the holder hereof. Maker shall notify Payee upon the
execution by Maker of any agreement relating to a proposed Financing. At the
closing of any Financing, Maker shall remit to Payee, by wire transfer of
immediately available funds on the same Business Day (or the next Business Day
if not reasonably practicable) as the closing of such Financing, an amount (to
be applied as a prepayment with respect hereto) equal to the lesser of (a) the
sum of the outstanding unpaid principal balance hereof and all accrued unpaid
interest thereon, and (b) the net cash proceeds from the Financing. All amounts
repaid or prepaid (including payments resulting from a Financing) shall be
applied first to earned, accrued and unpaid interest hereon and the balance, if
any, shall be applied to the outstanding principal.

         5.       The terms set forth below shall have the meanings assigned to
such terms as used in this Note:

                  "Applicable Law" shall mean the law in effect from time to
         time and applicable to the transactions between Payee and Maker
         pursuant to this Note that

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         lawfully permits the charging and collection of the highest permissible
         lawful non-usurious rate of interest on such transactions, including
         laws of the State of Texas, and to the extent controlling and providing
         for a higher lawful rate of interest, laws of the United States of
         America. It is intended that Chapter 1D, Subtitle 1, Title 79, Revised
         Civil Statutes of Texas, 1925, as amended, shall be included in the
         laws of the State of Texas in determining Applicable Law; and for the
         purpose of applying said Chapter 1D, the interest ceiling applicable to
         such transactions under said Chapter 1D shall be the indicated (weekly)
         rate ceiling from time to time in effect.

                  "Business Day" shall mean any day on which banks are open for
         general banking business in the State of Texas, other than on Saturday,
         Sunday, a legal holiday or any other day on which banks in the State of
         Texas are required or authorized by law or executive order to close.

                  "Credit Facility" shall mean one or more credit facilities
         providing for aggregate borrowings and other financial accommodations,
         including without limitation letter of credit facilities and related
         reimbursement obligations, of up to $100,000,000 that now is or are, or
         hereafter may be, entered into by Maker or any of its direct or
         indirect subsidiaries and the lenders party thereto, including any
         related notes, guarantees, collateral documents, reimbursement
         agreements and other instruments and agreements executed in connection
         therewith, which credit facility may be guaranteed by Maker or secured
         by all or part of the assets of Maker and its direct or indirect
         assets, in each case as may be amended, modified, supplemented,
         renewed, extended, refunded, replaced, restated or refinanced from time
         or time in whole or in part in one or more credit agreements, loan
         agreements, instruments or similar agreements so long as the aggregate
         permitted borrowings do not exceed $100,000,000.

                  "Financing" shall mean any transaction or series of related
         transactions (whether by means of the issuance and sale of debt or
         equity securities or a sale of assets or equity interests in another
         entity) pursuant to which Maker receives cash proceeds, net of
         underwriting fees and discounts and transaction expenses, of not less
         than $5,000,000; provided that none of the following transactions shall
         be deemed to be a "Financing": (a) any sale of assets in the ordinary
         course of Maker's business, (b) any borrowings or advances under the
         Credit Facility, (c) any issuances of securities pursuant to employee
         benefit plans or options granted thereunder, or (d) any borrowings not
         requiring the prior written consent of Payee pursuant to Section 6(l)
         of this Note.

                  "Indebtedness for Borrowed Money" shall mean any indebtedness
         of Maker or its subsidiaries for borrowed money; provided, however, the
         following shall not be considered Indebtedness for Borrowed Money:

                  (a)      indebtedness under this Note;


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                  (b)      indebtedness and other obligations from time to time
                           outstanding under, or guaranty obligations of Maker
                           or its Subsidiaries with respect to, the Credit
                           Facility;

                  (c)      intercompany indebtedness from time to time
                           outstanding between or among any of Maker and/or its
                           subsidiaries;

                  (d)      any indebtedness outstanding on the date of issuance
                           of this Note;

                  (e)      indebtedness, the net proceeds of which are used
                           solely to renew, extend, refinance, refund or
                           repurchase Indebtedness for Borrowed Money otherwise
                           permitted under this definition; provided, however,
                           such indebtedness shall not have terms and conditions
                           materially adverse to the creditworthiness of Maker
                           and its subsidiaries taken as a whole;

                  (f)      daylight overdraft facilities having customary terms
                           for such facilities; provided that such indebtedness
                           is extinguished or repaid within two Business Days
                           of incurrence;

                  (g)      credit facilities, established in connection with
                           customary cash management procedures, for up to
                           $1,000,000, to permit use of wire transfer facilities
                           and to cover checks and other payments made to the
                           order of Maker or its subsidiaries for which
                           immediate bank account credit is given but for which
                           customary clearing times may exceed two Business
                           Days;

                  (h)      credit facilities of up to $3,000,000 established to
                           facilitate cash management functions on customary
                           terms, in connection with automated clearing house
                           (ACH) transactions for payroll for Maker or its
                           subsidiaries;

                  (i)      accounts and other trade payables incurred in the
                           ordinary course of business and any standby letters
                           of credit, bid, performance or surety bonds or other
                           reimbursement obligations issued for the account of,
                           or entered into by, Maker or any of its subsidiaries
                           in the ordinary course of business; and

                  (j)      capitalized lease obligations incurred in the
                           ordinary course of business or purchase money
                           indebtedness incurred in the ordinary course of
                           business (so long as such capitalized lease
                           obligations and purchase money indebtedness do not
                           exceed $7,500,000 at any one time in the aggregate).

                  "Material Subsidiary" shall mean a direct or indirect majority
         owned subsidiary of Maker with total assets exceeding $5,000,000.

                  "Maximum Rate" shall mean the maximum lawful non-usurious rate
         of interest, if any, that under Applicable Law Payee is permitted to
         charge Maker on the loan evidenced by this Note from time to time. If,
         however, during any period interest accruing on this Note is not
         limited to any maximum lawful non-usurious rate of interest under
         Applicable Law, then during each such period the "Maximum Rate" shall
         be equal to a per annum rate of 4% plus the Note Rate.

                  "Note Rate" shall mean a per annum rate of interest (computed
         on the basis of the actual number of days elapsed (including the first
         but excluding the last day) over a year of 365 or 366 days, as the case
         may be) equal to 10%.

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                  "Subordination Agreement" shall mean a subordination agreement
         between Maker, certain subsidiaries of Maker (as may be required under
         the circumstances of the Credit Facility), Payee and the lenders under
         the Credit Facility (or such lenders agent, as the case may be)
         providing for the subordination of Payee's rights and obligations under
         this Note to the rights of such lenders under the Credit Facility,
         which subordination agreement shall contain terms and conditions that
         are normal and customary in agreements of this type and acceptable to
         Payee in its reasonable discretion.

         6.       If any one of the following events shall occur and be
continuing (an "Event of Default"):

                  (a)      Maker shall fail to pay timely when due, the
         principal of, or accrued unpaid interest on, this Note or any other of
         the obligations hereunder within three Business Days following the due
         date;

                  (b)      Maker or any Material Subsidiary shall (i) dissolve
         or terminate its existence, (ii) merge with or into any other entity
         (other than a wholly-owned subsidiary (excluding director qualifying
         shares or other immaterial ownership required by applicable law) of
         Maker) after the date hereof, (iii) discontinue its usual business or
         (iv) sell all or substantially all of its business or assets;

                  (c)      Maker or any Material Subsidiary shall (i) apply for
         or consent to the appointment of a receiver, trustee, custodian or
         liquidator of it or of all or a substantial part of its property, (ii)
         generally fail to pay its debts as they come due in the ordinary course
         of business or (iii) commence, or file an answer admitting the material
         allegations of or consenting to, or default in a petition filed against
         it in, any case, proceeding or other action under any existing or
         future law of any jurisdiction, domestic or foreign, relating to
         bankruptcy, insolvency, reorganization or relief of debtors, or seeking
         to have an order for relief entered with respect to it under the
         federal Bankruptcy Code 11 USC Section 101 et. seq., or seeking
         reorganization, arrangement, adjustment, winding-up, liquidation,
         dissolution, composition or the similar relief with respect to it or
         its debt;

                  (d)      Any person or group becomes the beneficial owner (as
         such terms are defined in the rules promulgated under the Securities
         Exchange Act of 1934) of 40% or more of the voting power of Maker's
         capital stock or shall otherwise have the right to cast 40% or more of
         the votes cast in any election of Maker's directors (excluding votes
         cast by or at the direction of directors of the Company by means of
         proxies solicited in accordance with the Securities Exchange Act of
         1934);

                  (e)      A receiver, conservator, liquidator, custodian or
         trustee of Maker or any Material Subsidiary or any of its property is
         appointed by the order or decree of any court or agency or supervisory
         authority having jurisdiction; or Maker obtains an order for relief
         under the federal Bankruptcy Code 11 USC Section 101 et. seq.; or any
         of the property of Maker is sequestered by court order; or a petition
         is filed or a proceeding is commenced against Maker or any Material
         Subsidiary under any


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         bankruptcy, reorganization, arrangement, insolvency, readjustment of
         debt, dissolution or liquidation law of any jurisdiction, whether now
         or hereafter in effect;

                  (f)(1)   Any event or condition occurs that results in the
         occurrence of any event, circumstance or condition that, after any
         applicable cure or notice period or lapse of time, or both, would
         constitute a default under the Credit Facility that continues
         unremedied for any applicable cure period, whether or not a party
         thereto exercises any of its rights and remedies with respect to such
         default;

                  (g)      The levy or execution of any attachment, execution or
         other process against any material property or interest in property of
         Maker or any Material Subsidiary that is not timely and completely
         stayed by appropriate proceedings and/or bonding requirements;

                  (h)      Any court shall find or rule, or Maker or any
         Material Subsidiary shall assert or claim, that this Note does not or
         will not constitute the legal, valid, binding and enforceable
         obligations of the party or parties hereto;

                  (i)      The rendering of any judgment or judgments against
         Maker or any Material Subsidiary for the payment of money in excess of
         $5,000,000, in the aggregate, that remains unsatisfied and in effect
         for any period of 60 consecutive days without a stay of execution;

                  (j)      Maker or any Material Subsidiary shall have
         concealed, removed, or permitted to be concealed or removed, any part
         of its property, with intent to hinder, delay or defraud its creditors
         or any of them, or made or suffered a transfer of any of its property
         that may be fraudulent under any bankruptcy, fraudulent conveyance or
         similar law; or shall have made any transfer of its property to or for
         the benefit of a creditor at a time when other creditors similarly
         situated have not been paid; or shall have suffered or permitted, while
         insolvent, any creditor to obtain a lien upon any of its property
         through legal proceedings or distraint or other process that is not
         vacated within 15 days from the date thereof;

                  (k)      Maker shall declare, set aside or pay any dividend or
         distribution of any kind (in cash, property, securities or otherwise)
         (but excluding dividends or distributions of common stock);

                  (l)      Maker and its subsidiaries shall have outstanding, at
         any one time, without the prior written consent of Payee, Indebtedness
         for Borrowed Money exceeding in the aggregate $100,000,000; or

                  (m)      Maker shall breach any material provision of the
         Subordination Agreement;

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then Payee, at its option, subject to the Subordination Agreement, may declare
the unpaid principal portion of this Note to be forthwith due and payable,
whereupon the said portion of this Note and all accrued, earned and unpaid
interest shall become immediately due and payable by Maker without demand,
presentment for payment, notice of non-payment, protest, notice of protest,
notice of intent to accelerate maturity, notice of acceleration of maturity or
any other notice of any kind to Maker, or any other person liable hereon or with
respect hereto, all of which are hereby expressly waived by Maker and each other
person liable hereon or with respect hereto, anything contained herein or in any
other documents or instruments to the contrary notwithstanding; and upon the
happening of any Event of Default referred to in paragraphs (b), (c), (d) or
(e), the unpaid principal portion of this Note and all other interest on this
Note then accrued, earned and unpaid shall become automatically due and payable
by Maker without demand, presentment for payment, notice of nonpayment, protest,
notice of protest, notice of intent to accelerate maturity, notice of
acceleration of maturity or any other notice of any kind to Maker or any other
person liable hereon or with respect hereto, all of which are expressly waived
by Maker and each other Person liable hereon or with respect hereto, anything
contained herein or in any document or instrument to the contrary
notwithstanding. Further, upon any default or event of default, subject to the
Subordination Agreement, Payee shall have all other rights and remedies as set
forth herein and as otherwise provided at law or in equity, all such rights and
remedies being cumulative, including, but without limitation, the right, without
prior notice to Maker or any other person liable with respect hereto, to set-off
and apply any indebtedness at any time owing by Payee to, or for the credit or
account of, Maker against any indebtedness owed to Payee by Maker, irrespective
of whether or not Payee shall have made demand under this Note or any other
instrument securing this Note, and although this Note may not then be matured;
provided, that any exercise of said set-off by Payee shall be subsequently
followed by notice from Payee to Maker of such right exercised, but the failure
to give such notice shall in no manner affect the right of Payee in respect to
set-offs and corresponding applications of funds.

         7.       Upon the execution by Maker of any agreement related to a
proposed Financing, Maker shall promptly provide written notice thereof to
Payee's Chief Financial Officer.

         8.       Maker shall, upon demand by Payee, promptly pay to Payee any
and all costs and expenses, including legal expenses, collections costs and
attorneys' fees (whether or not legal proceedings are instituted including,
without limitation, legal expenses and reasonable attorneys' fees in connection
with any bankruptcy proceedings), incurred or paid by Payee in protecting or
enforcing Payee's rights hereunder. Without limiting the generality of the
foregoing, if this Note is collected by suit or through the Bankruptcy Court, or
any judicial proceeding, or if this Note is not paid at maturity, however such
maturity may be brought about, and it is placed in the hands of an attorney for
collection (whether or not legal proceedings are instituted), then Maker agrees
to pay, in addition to all other amounts owing hereunder, the collection costs
and reasonable attorneys' fees of the holder hereof. The obligations of Maker
hereunder shall be subject to the provisions of the Subordination Agreement.

         9.       The records of Payee shall constitute rebuttably presumptive
evidence of the principal and earned, accrued and unpaid interest remaining
outstanding on this Note.

         10.      It is the intent of Payee and Maker in the execution and
performance of this Note to remain in strict compliance with Applicable Law from
time to time in effect. In furtherance thereof,

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Payee and Maker stipulate and agree that none of the terms and provisions
contained in this Note shall ever be construed to create a contract to pay for
the use, forbearance or detention of money with interest at a rate or in an
amount in excess of the Maximum Rate or amount of interest permitted to be
charged under Applicable Law. For purposes of this Note "interest" shall include
the aggregate of all charges that constitute interest under Applicable Law that
are contracted for, charged, reserved, received or paid under this Note. Maker
shall never be required to pay unearned interest and shall never be required to
pay interest at a rate or in an amount in excess of the Maximum Rate or amount
of interest that may be lawfully charged under Applicable Law, and the
provisions of this paragraph shall control over all other provisions of this
Note, and of any other instrument pertaining to or securing this Note, that may
be in actual or apparent conflict herewith. If this Note is prepaid, or if the
maturity of this Note is accelerated for any reason, or if under any other
contingency the effective rate or amount of interest that would otherwise be
payable under this Note would exceed the Maximum Rate or amount of interest
Payee or any other holder of this Note is allowed by Applicable Law to charge,
contract for, take, reserve or receive, or in the event Payee or any holder of
this Note shall charge, contract for, take, reserve or receive monies that are
deemed to constitute interest that would, in the absence of this provision,
increase the effective rate or amount of interest payable under this Note to a
rate or amount in excess of that permitted to be charged, contracted for, taken,
reserved or received under Applicable Law then in effect, then the principal
amount of this Note or the amount of interest that would otherwise be payable
under this Note or both shall be reduced to the amount allowed under Applicable
Law as now or hereinafter construed by the courts having jurisdiction, and all
such moneys so charged, contracted for, taken, reserved or received that are
deemed to constitute interest in excess of the Maximum Rate or amount of
interest permitted by Applicable Law shall immediately be returned to or
credited to the account of Maker upon such determination. Payee and Maker
further stipulate and agree that, without limitation of the foregoing, all
calculations of the rate or amount of interest contracted for, charged, taken,
reserved or received under this Note that are made for the purpose of
determining whether such rate or amount exceeds the Maximum Rate or amount,
shall be made to the extent not prohibited by Applicable Law, by amortizing,
prorating, allocating and spreading during the period of the full stated term of
this Note, all interest at any time contracted for, charged, taken, reserved or
received from Maker or otherwise by Payee or any other holder of this Note.

         11.      Maker and all sureties, endorsers and guarantors, if any
(which shall not include any obligor under the Credit Facility that is not a
party to the Subordination Agreement), of this Note waive demand, presentment
for payment, notice of non-payment, protest, notice of protest, notice of intent
to accelerate maturity, notice of acceleration of maturity and all other notice,
filing of suit and diligence in collecting this Note or enforcing any security
herefor, and agree to any substitution, exchange or release of any such
security, the release of any party primarily or secondarily liable hereon and
further agree that it will not be necessary for any holder hereof, in order to
enforce payment of this Note, to first institute suit or exhaust its remedies
against any security herefor, and consent to any one or more extensions or
postponements of time of payment of this Note on any terms or any other
indulgences with respect hereto, without notice thereof to any of them.

         12.      This Note shall be governed by and construed in accordance
with the internal laws of the State of Texas and applicable federal laws of the
United States of America. This Note has been delivered and accepted and is
payable at Houston, Harris County, Texas. There are no unwritten or oral
agreements between Maker and Payee. Payee has no commitment to make any

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additional loans or extend financial accommodations to Maker beyond the
indebtedness evidenced hereby.

         EXECUTED AND EFFECTIVE as of the day and year first above written.

                                     MAKER:

                                     GRANT PRIDECO, INC.



                                     By: /s/ John C. Coble
                                        --------------------------------
                                             John C. Coble
                                             President


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