AGREEMENT --------- The Bank and the Borrower agree to modify the Loan Agreement as follows:

Exhibit 10.1
MODIFICATION TO
COMMERCIAL REVOLVING LOAN AND SECURITY AGREEMENT

THIS MODIFICATION TO COMMERCIAL REVOLVING LOAN AND SECURITY AGREEMENT (the
"Modification Agreement") is made as of April 20, 1999, by and between FLEET
NATIONAL BANK, a national banking association having an address at ▇▇▇ ▇▇▇▇▇▇▇▇
▇▇▇▇▇▇, ▇▇▇▇▇▇▇▇, ▇▇▇▇▇▇▇▇▇▇▇ ▇▇▇▇▇ (the "Bank"), BOLT TECHNOLOGY CORPORATION, a
Connecticut corporation with an office at Four ▇▇▇▇ ▇▇▇▇▇, ▇▇▇▇▇▇▇, ▇▇▇▇▇▇▇▇▇▇▇
▇▇▇▇▇ (the "Borrower"), CUSTOM PRODUCTS CORPORATION, formerly known as Custom
Acquisition Corporation, BOLT INTERNATIONAL CORPORATION, DUKE PLACE INVESTMENTS,
BOLT EXPORT CORPORATION, CRITERION EXPLORATION, INC., STAR GEOPHYSICAL
CORPORATION, and K&B RESOURCES, INC., all with an address of Four ▇▇▇▇ ▇▇▇▇▇,
▇▇▇▇▇▇▇, ▇▇▇▇▇▇▇▇▇▇▇ ▇▇▇▇▇ (collectively, the "Guarantor").

BACKGROUND
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On January 5, 1998, the Bank and the Borrower entered into a Commercial
Revolving Loan and Security Agreement (the "Loan Agreement") whereby the Bank
made available to the Borrower a reducing loan facility in the maximum principal
amount of $3,500,000.00 by way of a revolving line of credit (the "Revolving
Loan"). The Revolving Loan is evidenced by a Commercial Revolving Promissory
Note dated January 5, 1998 (the "Note"). In accordance with the terms of the
Note, the maximum principal amount currently available to the Borrower
under the

Revolving Loan is $3,000,000.00. The Guarantors have unconditionally guarantied
all indebtedness of Borrower to Bank including, without limitation, the
Revolving Loan.

The Loan Agreement restricts the Borrower, inter alia, from permitting any
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liens against its properties or assets, incurring any additional indebtedness,
or consolidating or merging with any other corporation or entity, except as may
be permitted under the Loan Agreement. The Borrower now wishes to acquire 100%
of the capital stock of AG Geophysical, Inc. ("AG"), a Texas based manufacturer,
for the total purchase price of $13,600,000.00 (the AG Acquisition"). A portion
of the AG Acquisition purchase price is to be financed by a $7,000,000.00
promissory note from the Borrower in favor of ▇▇ ▇▇▇▇▇▇▇, sole shareholder of AG
(the "Gerrans Note"). The Gerrans Note is to be secured by AG's grant of a
security interest in the assets of AG in favor of ▇▇ ▇▇▇▇▇▇▇, and by the
Borrower's pledge of the AG stock being purchased from ▇▇ ▇▇▇▇▇▇▇. The Borrower
has requested the Bank to modify the Loan Agreement in order to permit the
acquisition and the granting of the security interest, and the Bank is
agreeable, all upon the terms to follow.

AGREEMENT
---------
The Bank and the Borrower agree to modify the Loan Agreement as follows:

1. ENCUMBRANCES. Paragraph 6.03(a) of the Loan Agreement is hereby
------------
amended to provide that the Borrower may cause AG to

grant a security interest in AG's assets in favor of ▇▇ ▇▇▇▇▇▇▇ to secure the
Borrower's obligations under the Gerrans Note.

2. LIMITATION ON INDEBTEDNESS. Paragraph 6.03(b) of the Loan Agreement
--------------------------
is hereby amended to provide that the Borrower may incur up to $7,000,000.00 in
seller financing in connection with the AG Acquisition.

3. LOANS, ADVANCES, INVESTMENTS. Paragraphs 6.03(e) and 6.03(q) of the
----------------------------
Loan Agreement are hereby amended to provide that the Borrower may use the
proceeds of the Revolving Loan to purchase the AG stock.

4. USE OF LOAN PROCEEDS. Paragraph 6.03(k) of the Loan Agreement is
--------------------
hereby amended to provide that the Borrower may also use the proceeds of the
Revolving Loan for the AG Acquisition.

5. BUSINESS OPERATIONS. Paragraph 6.03(n) of the Loan Agreement is
-------------------
hereby amended to provide that the Borrower may also engage in the business
conducted through AG, its wholly owned subsidiary.

6. FINANCIAL COVENANTS. Paragraphs 6.04(a) and 6.04(c) of the Loan
-------------------
Agreement are hereby deleted in their entirety and replaced with the following:
(a) Minimum Tangible Net Worth. Permit its Tangible Net Worth to be
--------------------------
less than $4,275,000.00 at any time. At the Borrower's fiscal year end of June
30, 1999, this level must increase by an amount equal to 75% of the Borrower's
net income for the period from January 1, 1999, through June 30, 1999. Beginning
with the Borrower's fiscal year end of June 30, 2000, this level must increase
each year by an amount equal to 75% of the Borrower's annual net income. This
covenant shall be tested quarterly.

(c) Total Liabilities/Tangible Net Worth. Permit the ratio of its
------------------------------------
Total Liabilities to Tangible Net Worth to be greater than (i) 3.00 to 1.00 at
any time up through and including fiscal quarter ending December 31, 1999, (ii)
2.00 to 1.00 at any time subsequent to fiscal quarter ending December 31, 1999,
but up through and including fiscal quarter ending December 31, 2000, and (iii)
1.25 to 1.00 at any time subsequent to fiscal quarter ending December 31, 2000.
This covenant shall be tested quarterly.

7. FUTURE GRANT OF COLLATERAL. Article VII of the Loan Agreement is
--------------------------
hereby deleted in its entirety and replaced with the following:

The Borrower and the Guarantor hereby pledges, assigns, transfers, and
grants to the Bank a lien and security interest in all of their business
assets including, but not limited to, all Accounts, Chattel Paper,
Documents, Equipment, General Intangibles, Instruments, Inventory
(including work in process), as those terms are defined in the Uniform
Commercial Code, together with all proceeds thereof, in order to secure the
prompt payment and performance of the Obligations, as such term is defined
in the Loan Agreement, which security interests shall only attach and
automatically become effective in the event (a) the Borrower fails to make
a contingent payment required to be made under the Asset Purchase Agreement
dated as of November 14, 1997, by and among the Borrower, Custom Products
Corporation, ▇▇▇▇▇▇ ▇▇▇▇▇ and ▇▇▇▇▇▇ ▇▇▇▇▇, or (b) the Gerrans Note is
accelerated due to a default thereunder (each of the foregoing events is
hereinafter referred to as a "Triggering Event"). Any such Triggering
Event shall be an Event of Default under the Loan Agreement. Borrower and
Guarantor shall each execute a UCC-1 financing statement contemporaneously
with this Agreement which shall be held by Bank's counsel in escrow, to be
filed only upon delivery by Bank of a notice certifying that a Triggering
Event has occurred (a copy of which shall also be delivered simultaneously
by the Bank to Borrower). Upon such filing, the UCC-1 financing statements
shall serve to automatically perfect the security interests granted to the
Bank upon such Triggering Event. This Article VII shall automatically
expire, and the lien and security interest provided herein, and be of no
further force and effect upon the date on which both (a) no further such
contingent payments are to be made under the referenced Asset Purchase
Agreement, and (b) the Gerrans Note has been fully satisfied. Upon such
expiration, the above referenced UCC-1 shall be returned to

the Borrower (or if previously filed, the Bank will file a termination
statement for such filing.

8. SCHEDULE 5(W). Schedule 5(w) of the Loan Agreement is hereby amended
-------------
to include AG Geophysical, Inc. as a subsidiary of the Borrower.

9. EVENTS OF DEFAULT. Paragraphs 8.01(g) and 8.01(h) of the Loan
-----------------
Agreement are hereby amended to allow AG to ▇▇▇▇▇ ▇ ▇▇▇▇ and security interest
in its assets to ▇▇ ▇▇▇▇▇▇▇ in order to secure the Gerrans Note.

10. YEAR 2000 RISK. Borrower has reviewed the "Year 2000 Risk" (that is
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the risk that computer applications used by Borrower may be unable to recognize
and perform without error date-sensitive functions involving certain dates prior
to and any date after December 31, 1999) and represents that it is taking such
action as may be necessary to insure that the Year 2000 Risk will not adversely
affect its business operations and/or financial conditions.

11. REAFFIRMATION OF BORROWER. Borrower hereby acknowledges and reaffirms
-------------------------
the Revolving Loan and its liability for payment thereof. Borrower agrees,
represents, and warrants that (a) no setoff, counterclaim, or defense exists
with respect to its liability under the Revolving Loan and that no other claim
against the Bank exists and waives its right to raise any such setoff,
counterclaim, defense, or claim against the Bank arising out of occurrences on
or prior to the date hereof, (b) all the representations and warranties
contained in the Loan Agreement,

after giving effect to the amendments and modifications contemplated hereby, are
true and correct on and as of the date hereof as though made on and as of the
date hereof, (c) the Borrower has taken all corporate or other action necessary
to make this Modification Agreement and all agreements and instruments executed
in connection herewith the valid and enforceable obligations they purport to be,
and (d) no default or breach under the Loan Agreement after giving effect to the
amendments contemplated hereby, and no event which the passage of time or giving
of notice or both would constitute such a default or breach, exists on the date
hereof.

12. REAFFIRMATION OF GUARANTORS. Each Guarantor hereby acknowledges and
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reaffirms their respective Guaranty pursuant to, and in accordance with, the
terms thereof. Each Guarantor agrees that no setoff, counterclaim, or defense
exists with respect to his, her, or its liability under such Guaranty and that
no other claim against the Bank exists and waives its right to raise any such
setoff, counterclaim, defense, or claim against the Bank arising out of
occurrences on or prior to the date hereof. Each Guarantor agrees that in the
event a security interest is granted to the Bank, the Bank shall have the same
rights and remedies against the Guarantor as it has against the Borrower under
the Loan Agreement.

13. CONSENT OF GUARANTORS. Without limiting the generality of the
---------------------
foregoing or of any Guaranty, each Guarantor acknowledges that it is fully aware
of and has consented to this Agreement, and

further acknowledges and agrees that, pursuant to the terms hereof and of the
Guaranties, it remains liable, jointly and severally, for the full amount of the
outstanding Revolving Loan, as amended hereby, and its obligations under its
respective Guaranty continues in full force and effect notwithstanding this
Modification Agreement which shall not, in any way, impair, discharge, or limit
the obligations of any Guarantor to the Bank arising hereunder or under the Loan
Agreement, as amended, or each such Guaranty. Each Guarantor reaffirms that the
provisions of this Modification Agreement shall not be construed as superseding
or limiting their respective Guaranty, each of which continues in full force and
effect. The terms hereof shall be an addition to, and not in lieu of, the terms
of their respective Guaranty.

14. OTHER CHANGES. All other terms and conditions of the Loan Agreement
-------------
shall remain the same and in full force and effect except as specifically
amended herein.

15. JURISDICTION. This Modification Agreement and all other agreements,
------------
documents, and instruments executed in connection herewith or contemplated
hereby shall be governed by and construed in accordance with the laws of the
State of Connecticut.

16. CAPTIONS. The captions are inserted herein only as a matter of
--------
convenience and for reference, and in no way define, limit, describe, or in any
way affect the scope or intent of this Modification Agreement.

17. JURY TRIAL WAIVER. THE BORROWER AND GUARANTORS WAIVE TRIAL BY JURY IN
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ANY COURT IN ANY SUIT, ACTION, PROCEEDING OR ANY MATTER ARISING IN CONNECTION
WITH OR IN ANY WAY RELATED TO THIS MODIFICATION AGREEMENT OR THE FINANCING
TRANSACTION OF WHICH THIS MODIFICATION AGREEMENT IS A PART OR THE DEFENSE OR
ENFORCEMENT OF ANY OF THE BORROWER'S AND GUARANTORS' RIGHTS AND REMEDIES IN
CONNECTION THEREWITH. THE BORROWER AND GUARANTORS ACKNOWLEDGE THAT THEY MAKE
THIS WAIVER KNOWINGLY, VOLUNTARILY, WITHOUT DURESS AND ONLY AFTER THE
OPPORTUNITY FOR EXTENSIVE CONSIDERATION OF THE RAMIFICATIONS OF THIS WAIVER WITH
THEIR ATTORNEYS. THIS WAIVER CONSTITUTES A MATERIAL INDUCEMENT FOR THE BANK TO
EXTEND THIS FINANCING COMMITMENT AND TO ENTER INTO THIS MODIFICATION AGREEMENT
WITH RESPECT TO THE REVOLVING LOAN.

Executed to be effective as of the date first set forth above.
THE BORROWER:
Signed in the presence of: BOLT TECHNOLOGY CORPORATION
(As to All)

By: /s/▇▇▇▇▇▇▇ ▇.▇▇▇▇
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__________________________ ▇▇▇▇▇▇▇ ▇. ▇▇▇▇
Its President, duly authorized

__________________________

THE BANK:

FLEET NATIONAL BANK

By /s/ ▇▇▇▇▇▇ ▇. ▇▇▇▇▇▇
-----------------------
▇▇▇▇▇▇ ▇. ▇▇▇▇▇▇
Its Vice President

THE GUARANTORS:

CUSTOM PRODUCTS CORPORATION, formerly known as,
CUSTOM ACQUISITION CORPORATION