<PAGE>

                                 EXHIBIT 10.6.3


U.S.  BANK CREDIT FACILITY
<TABLE>

                                 PROMISSORY NOTE
<CAPTION>

-------------------- ---------------- --------------- ------------- -------- -------------- ----------------- ----------- ----------
     PRINCIPAL          LOAN DATE        MATURITY       LOAN NO.     CALL     COLLATERAL        ACCOUNT        OFFICER    INITIALS
<S>                    <C>              <C>               <C>                     <C>          <C>              <C>
   $5,500,000.00       02-15-2001       10-15-2001        2784                    70           1105510939       DJS64
-------------------- ---------------- --------------- ------------- -------- -------------- ----------------- ----------- ----------

REFERENCES IN THE SHADED AREA ARE FOR LENDER'S USE ONLY AND DO NOT LIMIT THE APPLICABILITY OF THIS DOCUMENT TO ANY PARTICULAR LOAN
OR ITEM
------------------------------------------------------------------------------------------------------------------------------------

BORROWER:      HI-SHEAR TECHNOLOGY, CORP.                              LENDER:    U.S. BANK NATIONAL ASSOCIATION
               24225 GARNIER ST.                                                  4100 NEWPORT PLACE, SUITE 120
               TORRANCE, CA  90505                                                NEWPORT BEACH, CA  92660

====================================================================================================================================
</TABLE>

PRINCIPAL AMOUNT: $5,500,000.00                  DATE OF NOTE: FEBRUARY 15, 2001

PROMISE TO PAY. Hi-Shear Technology, Corp. ("Borrower") promises to pay to U.S.
Bank National Association ("Lender"), or order, in lawful money of the United
States of America, the principal amount of Five Million Five Hundred Thousand &
00/100 Dollars ($5,500,000.00) or so much as may be outstanding, together with
interest on the unpaid outstanding principal balance of each advance. Interest
shall be calculated from the date of each advance until repayment of each
advance.

PAYMENT. Borrower will pay this loan on demand, or if no demand is made, in one
payment of all outstanding principal plus all accrued unpaid interest on October
15, 2001. In addition, Borrower will pay regular monthly payments of accrued
unpaid interest beginning March 1, 2001, and all subsequent interest payments
are due on the same day of each month after that. The annual interest on this
Note is computed on a 365/360 basis; that is, by applying the ratio of the
annual interest rate over a year of 360 days, multiplied by the outstanding
principal balance, multiplied by the actual number of days the principal balance
is outstanding. Borrower will pay Lender at Lender's address shown above or at
such other place as Lender may designate in writing.

VARIABLE INTEREST RATE. The interest rate on this Note is subject to change from
time to time based on changes in an independent index which is the Wall Street
Journal Prime Rate. This is the Prime Rate as published in the West Coast
edition of The Wall Street Journal "Money Rates" column (the "Index"). The Index
is not necessarily the lowest rate charged by Lender on its loans. If the Index
becomes unavailable during the term of this loan, Lender may designate a
substitute index after notice to Borrower. Lender will tell Borrower the current
Index rate upon Borrower's request. Borrower understands that Lender may make
loans based on other rates as well. The interest rate change will not occur more
often than each day. The interest rate to be applied to the unpaid principal
balance of this Note will be at a rate of 0.500 percentage points over the
Index. NOTICE: Under no circumstances will the interest rate on this Note be
more than the maximum rate allowed by applicable law.

PREPAYMENT. Borrower agrees that all loan fees and other prepaid finance charges
are earned fully as of the date of the loan and will not be subject to refund
upon early payment (whether voluntary or as a result of default), except as
otherwise required by law.

Except for the foregoing, Borrower may pay without penalty all or a portion of
the amount owed earlier than it is due. Early payments will not, unless agreed
to by Lender in writing, relieve Borrower of Borrower's obligation to continue
to make payments of accrued unpaid interest. Rather, they will reduce the
principal balance due.
<PAGE>

DEFAULT. Borrower will be in default if any of the following happens: (a)
Borrower fails to make any payment when due. (b) Borrower breaks any promise
Borrower has made to Lender, or Borrower fails to comply with or to perform when
due any other term, obligation, covenant, or condition contained in this Note or
any agreement related to this Note, or in any other agreement or loan Borrower
has with Lender. (c) Borrower defaults under any loan, extension of credit,
security agreement, purchase or sales agreement, or any other agreement, in
favor of any other creditor or person that may materially affect any of
Borrower's property or Borrower's ability to repay this Note or perform
Borrower's obligations under this Note or any of the Related Documents. (d) Any
representation or statement made or furnished to Lender by Borrower or on
Borrower's behalf is false or misleading in any material respect either now or
at the time made or furnished. (e) Borrower becomes insolvent, a receiver is
appointed for any part of Borrower's property, Borrower makes an assignment for
the benefit of creditors, or any proceeding is commenced either by Borrower or
against Borrower under any bankruptcy or insolvency laws. (f) Borrower is in
default under any other note, security agreement, lease agreement or lease
schedule, loan agreement or other agreement, whether now existing or hereafter
made, between Borrower and U.S. Bancorp or any direct or indirect subsidiary of
U.S. Bancorp. (g) Any creditor tries to take any of Borrower's property on or in
which Lender has a lien or security interest. This includes a garnishment of any
of Borrower's accounts with Lender. (h) Any guarantor dies or any of the other
events described in this default section occurs with respect to any guarantor of
this Note. (i) A material adverse change occurs in Borrower's financial
condition, or Lender believes the prospect of payment or performance of the
indebtedness is impaired.

LENDER'S RIGHTS. Upon default, Lender may declare the entire unpaid principal
balance on this Note and all accrued unpaid interest immediately due, without
notice, and then Borrower will pay that amount. Upon Borrower's failure to pay
all amounts declared due pursuant to this section, including failure to pay upon
final maturity, Lender, at its option, may also, if permitted under applicable
law, increase the variable interest rate on this Note to 5.500 percentage points
over the Index. Lender may hire or pay someone else to help collect this Note if
Borrower does not pay. Borrower also will pay Lender that amount. This includes,
subject to any limits under applicable law, Lender's attorneys' fees and
Lender's legal expenses whether or not there is a lawsuit, including attorneys'
fees and legal expenses for bankruptcy proceedings (including efforts to modify
or vacate any automatic stay or injunction), appeals, and any anticipated
post-judgment collection services. Borrower also will pay any court costs, in
addition to all other sums provided by law. This Note has been delivered to
Lender and accepted by Lender in the State of California. If there is a lawsuit,
Borrower agrees upon Lender's request to submit to the jurisdiction of the
courts of Sacramento County, the State of California. Lender and Borrower hereby
waive the right to any jury trial in any action, proceeding, or counterclaim
brought by either Lender or Borrower against the other. This Note shall be
governed by and construed in accordance with the laws of the State of
California.

LINE OF CREDIT. This Note evidences a revolving line of credit. Advances under
this Note as well as directions for payment from Borrower's accounts, may be
requested orally or in writing by Borrower or by an authorized person. Lender
may, but need not, require that all oral requests be confirmed in writing.
Borrower agrees to be liable for all sums either: (a) advanced in accordance
with the instructions of an authorized person or (b) credited to any of
Borrower's accounts with Lender. The unpaid principal balance owing on this Note
at any time may be evidenced by endorsements on this Note or by Lender's
internal records, including daily computer print-outs. Lender will have no
obligation to advance funds under this Note if: (a) Borrower or any guarantor is
in default under the terms of this Note or any agreement that Borrower or any
guarantor has with Lender, including any agreement made in connection with the
signing of this Note; (b) Borrower or any guarantor ceases doing business or is
insolvent; (c) any guarantor seeks, claims or otherwise attempts to limit,
modify or revoke such guarantor's guarantee of this Note or any other loan with
Lender; (d) Borrower has applied funds provided pursuant to this Note for
purposes other than those authorized by Lender.

LATE CHARGE. If a payment is 15 days or more past due, Borrower will be charged
a late charge of 5% of the delinquent payment.

GENERAL PROVISIONS. This Note is payable on demand. The inclusion of specific
default provisions or rights of Lender shall not preclude Lender's right to
declare payment of this Note on its demand. Lender may delay or forgo enforcing
any of its right or remedies under this Note without losing them. Borrower and
any other person who signs, guarantees or endorses this Note, to the extent
allowed by law, waive any applicable statute of limitations, presentment, demand
for payment, protest and notice of dishonor. Upon any change in the terms of
this Note, and unless otherwise expressly stated in writing, no party who signs
this Note, whether as maker, guarantor, accommodation maker or endorser, shall
be released from liability. All such parties agree that Lender may renew or
extend (repeatedly and for any length of time) this loan, or release any party
or guarantor or collateral; or impair, fail to realize upon or perfect Lender's
security interest in the collateral; and take any other action deemed necessary
by Lender without the consent of or notice to anyone. All such parties also
agree that Lender may modify this loan without consent of or notice to anyone
other than the party with whom the modification is made.
<PAGE>

PRIOR TO SIGNING THIS NOTE, BORROWER READ AND UNDERSTOOD ALL THE PROVISIONS OF
THIS NOTE, INCLUDING THE VARIABLE INTEREST RATE PROVISIONS. BORROWER AGREES TO
THE TERMS OF THE NOTE AND ACKNOWLEDGES RECEIPT OF A COMPLETED COPY OF THE NOTE.

BORROWER:

Hi-Shear Technology, Corp.

By:  /s/ George W. Trahan                          By:  /s/ Thomas R. Mooney
     -------------------------------               -----------------------------
     Authorized Officer                            Authorized Officer
     GEORGE W. TRAHAN, PRESIDENT/CEO/CO-CHAIRMAN   THOMAS R. MOONEY, CO-CHAIRMAN

LENDER:

U.S. Bank National Association


By   /s/  Linda E. Claire
     ---------------------------
     Authorized Officer



<PAGE>

<TABLE>

                           CHANGES IN TERMS AGREEMENT
<CAPTION>

-------------------- ---------------- --------------- -------------- ------- -------------- ----------------- ----------- ----------
     PRINCIPAL          LOAN DATE        MATURITY       LOAN NO.      CALL    COLLATERAL        ACCOUNT        OFFICER    INITIALS
<S>                                     <C>            <C>                        <C>          <C>              <C>
   $4,600,000.00                        10-15-2001     2784-83/125                70           1105510939       DJS64
-------------------- ---------------- --------------- -------------- ------- -------------- ----------------- ----------- ----------

REFERENCES IN THE SHADED AREA ARE FOR LENDER'S USE ONLY AND DO NOT LIMIT THE APPLICABILITY OF THIS DOCUMENT TO ANY PARTICULAR LOAN
OR ITEM
------------------------------------------------------------------------------------------------------------------------------------

BORROWER:      HI-SHEAR TECHNOLOGY, CORP.                              LENDER:    U.S. BANK NATIONAL ASSOCIATION
               24225 GARNIER ST.                                                  4100 NEWPORT PLACE, SUITE 120
               TORRANCE, CA  90505                                                NEWPORT BEACH, CA  92660

====================================================================================================================================
</TABLE>

PRINCIPAL AMOUNT: $4,600,000.00               DATE OF AGREEMENT: OCTOBER 1, 2001

DESCRIPTION OF EXISTING INDEBTEDNESS. THAT CERTAIN PROMISSORY NOTE EXECUTED BY
BORROWER ON FEBRUARY 15, 2001, IN THE ORIGINAL AMOUNT OF $5,500,000, AS IT MAY
HAVE BEEN AMENDED OR RENEWED FROM TIME TO TIME (THE NOTE).

DESCRIPTION OF CHANGE IN TERMS. FOR VALUABLE CONSIDERATION, THE BORROWER AND
LENDER HEREBY AGREE THAT THE TERMS OF THE NOTE ARE CHANGED AS FOLLOWS:

1. EFFECTIVE JULY 30, 2001, THE PRINCIPAL AMOUNT OF THE NOTE HAS BEEN DECREASED
BY $700,000.00, FROM $5,500,000.00 TO $4,800,000.00.

2. EFFECTIVE OCTOBER 1, 2001, THE PRINCIPAL AMOUNT OF THE NOTE WILL BE DECREASED
BY $200,000.00, FROM $4,800,000.00 TO $4,600,000.00.

CONTINUING VALIDITY. Except as expressly changed by this Agreement, the terms of
the original obligation or obligations, including all agreements evidenced or
securing the obligation(s), remain unchanged and in full force and effect.
Consent by Lender to this Agreement does not waive Lender's right to strict
performance of the obligation(s) as changed, nor obligate Lender to make any
future change in terms. Nothing in this Agreement will constitute a satisfaction
of the obligation(s). It is the intention of Lender to retain as liable parties
all makers and endorsers of the original obligation(s), including accommodation
parties, unless a party is expressly released by Lender in writing. Any maker or
endorser, including accommodation makers, will not be released by virtue of this
Agreement. If any person who signed the original obligation does not sign this
Agreement below, then all persons signing below acknowledge that this Agreement
is given conditionally, based on the representation to Lender that the
non-signing party consents to the changes and provisions of this Agreement or
otherwise will not be released by it. This waiver applies not only to any
initial extension, modification or release, but also to all such subsequent
actions.

PRIOR TO SIGNING THIS AGREEMENT, BORROWER READ AND UNDERSTOOD ALL THE PROVISIONS
OF THIS AGREEMENT. BORROWER AGREES TO THE TERMS OF THE AGREEMENT AND
ACKNOWLEDGES RECEIPT OF A COMPLETED COPY OF THE AGREEMENT.

BORROWER:
HI-SHEAR TECHNOLOGY CORP.
By:  /s/ George W. Trahan
     -------------------------------
     Authorized Officer
     George W. Trahan, President/CEO/Co-Chairman

By:  /s/ Gregory J. Smith
     -------------------------------
     Authorized Officer
     Gregory J. Smith, CFO & Vice President of Information Systems

LENDER:
U.S. Bank National Association
By   /s/ Linda E. Claire
     ---------------------------
     Authorized Officer