<PAGE>
 
                                                                   Exhibit 10.21



September 22, 1998



Mr. Bruce D. Atkinson
President
Control Devices, Inc.
228 Northeast Road
Standish, Maine  04084

Dear Bruce:

Fleet Bank of Maine is pleased to approve a $20,000,000.00 revolving line of
credit to Control Devices, Inc. This letter, when properly signed and accepted,
will constitute an agreement between Fleet Bank of Maine of Portland, Maine
(hereinafter referred to as "Bank"), which agrees to lend, and Control Devices,
Inc. of Standish, Maine (hereinafter referred to as "Borrower") which agrees to
borrow, in accordance with the following terms and conditions, in addition to
those as outlined in the loan documents:

BORROWER:  Control Devices, Inc.
---------            

PURPOSE: To provide funds for acquisition financing, working capital for the
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   company's ongoing operations or the issuance of commercial or standby
   letters of credit.

MAXIMUM AMOUNT: Twenty million and 00/100 dollars ($20,000,000.00),
---------------                           
   representing a $5,000,000.00 increase.

INTEREST RATE:   During the term of the proposed financing, the Borrower will
--------------                                 
   have three interest rate options. Under the three rate options, interest
   is payable monthly based on actual days outstanding over a 360 day year.
 
   1) 30, 60, 90, or 180 day London Interbank Offering Rate (LIBOR) plus
   1.50%.

   2) Fleet Bank of Maine's cost of funds plus 1.50% for borrowings of 30
   days or less.

   3) Fleet Bank of Maine's prime lending rate (currently 8.50%), adjusted
   daily.

COMPENSATING BALANCE REQUIREMENT: As consideration for this commitment,
---------------------------------                    
   Borrower agrees to maintain average collected demand deposit compensating
   balances of $500,000.00 with Fleet Bank of Maine at all times.
<PAGE>
 
Mr. Bruce D. Atkinson
September 22, 1998


TERM: On demand, with interest payable monthly. Payments not made within 10
-----                                    
   days of the due date will be assessed a late fee equal to 5% of the payment
   amount.

PREPAYMENT: There shall be no prepayment charge on such advances for which the
-----------                                  
   prime lending rate of interest is elected. If a fixed rate of interest is
   elected (even if the fixed rate date is elected in advance and while
   Borrower is paying interest at the variable rate), then a prepayment charge
   for such advances so elected shall be payable by Borrower to Bank utilizing
   a yield maintenance formula satisfactory to Bank.

COLLATERAL:  Unsecured.
------------       

DEPOSIT ACCOUNTS: As consideration for this loan, Borrower is to continue
-----------------                             
   maintaining its primary depository relationship with Fleet Bank of Maine
   during the term of this financing. If for any reason this relationship
   changes, Fleet Bank of Maine specifically reserves the right to review and
   modify the rate and term of the loan without waiving the demand feature
   thereof.

FINANCIAL STATEMENTS: During the term of this financing, Borrower will provide
---------------------                             
   to Bank its audited fiscal year end financial statements (10-K), prepared
   by a certified public accountant acceptable to Bank, within 120 days of its
   fiscal year end.  In addition, Borrower will also provide management
   prepared quarterly interim financial statements (10-Q) and covenant
   compliance certificates within 45 days from the end of each quarter and
   annual projections.

FINANCIAL COVENANTS: During the term of the proposed financing, the Borrower
--------------------                             
   and its subsidiaries will be required to maintain the following financial
   covenants, measured quarterly:

     * Minimum tangible net worth of $22,000,000 through 12/31/99 and
     $25,000,000 thereafter.

     * Maximum total debt to tangible net worth ratio of 1.00 to 1.

     * Minimum quarterly cash flow coverage ratio of 1.5X, measured as
   follows:

        Earnings before interest, taxes, depreciation and amortization
        --------------------------------------------------------------
        Current portion of long term debt + interest

AUTHORITY TO ACT: Borrower shall provide all evidence of its organization,
-----------------                             
   existence, legal good standing, and authority to enter into said
   transactions as may be required by Bank or its counsel.
<PAGE>
 
Mr. Bruce D. Atkinson
September 22, 1998


LEGAL & COSTS: Borrower shall be responsible for bearing the cost of all legal
--------------                                 
   work to document these transactions. All instruments executed and delivered
   in connection with the closing of the loan shall be in form and substance
   satisfactory to Bank's counsel. All other matters relating to the law shall
   be made to meet the satisfaction of such counsel. All costs incurred by
   Bank to document these transactions will be borne by Borrower, regardless
   of whether the loan is actually closed or the financing consummated.

WRITTEN MODIFICATION: Borrower may not maintain any action against the Bank on
---------------------                             
   any agreement to lend money, extend credit, forbear from collection of a
   debt or make any other accommodation for repayment of a debt for more than
   $250,000 unless the promise, contract or agreement is in writing and signed
   by a duly authorized representative of Bank.

NONASSIGNABILITY OF COMMITMENT: This commitment is expressly offered only to
-------------------------------                       
   Borrower and only for the purposes described herein. This commitment may
   not be assigned without the written permission of Fleet Bank of Maine.

YEAR 2000: This commitment is subject to, among other conditions contained
---------                                 
   herein, the Borrower's demonstration to the satisfaction of Bank that (a)
   the Borrower has taken and is taking all necessary and appropriate steps to
   ascertain the extent of and successfully address business and financial
   risks facing the Borrower as a result of the Year 2000 Risk (that is the
   risk that computer applications used by Borrower and/or by its suppliers,
   vendors and customers 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 (b) the Borrower's material computer
   applications and those of its key vendors and suppliers will, on a timely
   basis, adequately address the Year 2000 Risk in all material respects.

EXPIRATION DATE: The revolving line of credit is available for your use through
----------------                                
   September 30, 2000, and is subject to review prior to renewal. However,
   Bank shall be under no obligation hereunder unless acceptance of the terms
   hereof is delivered to it by September 30, 1998.

The parties hereto agree that this commitment shall survive any loan closings
under this commitment and that each of the obligations and undertakings of
Borrower hereunder shall be continuing and shall not cease until the entire
loan, together with interest is paid in full.

This commitment may be terminated by Bank at any time upon discovery, by Bank,
of a material adverse change in or any misrepresentations or erroneous
statements about Borrower's position with respect to solvency, credit
worthiness, government regulation, or any other substantial factor. Such
termination shall become effective upon the mailing of notice of termination by
Bank by certified first-class mail to Borrower at the address shown on this
commitment.
<PAGE>
 
Mr. Bruce D. Atkinson
September 22, 1998



If you are in agreement with these terms, please acknowledge your acceptance of
this commitment by signing and returning the original of this letter. You may
retain a signed copy for your records.

Sincerely,


Peter C. Sylvestre
Vice President



                                ACCEPTED AND ACKNOWLEDGED:
 
                                Control Devices, Inc.

Date:______________             By:___________________________________
                                   Bruce D. Atkinson, President
<PAGE>
 
                                FIRST AMENDMENT
                                      TO
                                LOAN AGREEMENT

     THIS FIRST AMENDMENT TO LOAN AGREEMENT, dated as of September 30, 1998,
between CONTROL DEVICES, INC., an Indiana corporation with its principal place
of business in Standish, Maine ("Borrower") and FLEET BANK OF MAINE, a Maine
financial institution ("Bank").,

WITNESSETH:
     WHEREAS, Borrower and Bank are parties to a Loan agreement dated as of
October 8, 1996, (the "Loan Agreement"): and
     WHEREAS, Borrower and Bank desire to amend the Loan Agreement;
     NOW, THEREFORE, for valuable consideration, the receipt and sufficiency of
which are hereby acknowledged, Borrower and Bank hereby agree as follows:
     1.  Section 1(a) of the Loan Agreement is hereby deleted and replaced with
         following:

Subject to the terms and provision of this Agreement, Bank hereby establishes a
line of credit in Borrower's favor in the principal amount of up to Twenty
Million Dollars ($20,000,000) (the "Line of Credit").  The Line of Credit will
be available, subject to the terms hereof, until September 30, 2000, when the
Line of Credit, if not previously extended in writing by Bank, shall be
terminated and all amounts outstanding thereunder shall be paid in full.

     2.  The reference in Section 6 (g) of the Loan Agreement to "$350,000"
         shall be deleted and replaced with a reference to "$500,000".

     3.  The following shall be added as a new subsection (i) to Section 6 of
     the Loan Agreement:

     (i) Borrower shall, upon written request therefor by Bank to Borrower,
     which request may be withdrawn and remade from time to time at the sole
     discretion of Bank furnish Bank, on a quarterly basis, as soon as
     available, and in any event within (10) days after the end of each quarter,
     an updated status report, all in reasonable detail, by a representative of
     Borrower which is acceptable to Bank, reporting on the current status of
     the Borrower's computer system as it relates to the Year 2000 computer
     problem, which report shall also include estimated time, costs and budget
     allocations for completing any purchases, renovations or reprogramming
     which may be necessary for Borrower to become Year 2000 Compliant without
     any material interruption in the Borrower's business, financial condition
     or prospects.

     4.  Section 7 (a) of the Loan Agreement shall be deleted and replaced with
     the following:
         Minimum Tangible Net Worth: permit its tangible net worth, measured as
         of the end of each of Borrower's fiscal quarters, to be less than
         $22,000,000, through December 31, 1999 or less than $25,000,000
         thereafter, as shown on Borrower's financial statements;
 
     5.  Section 13 of the Loan Agreement is hereby amended by adding the
     following to the end thereof:
         (k) Bank may at any time pledge all or any portion of its rights
     under the loan documents including any portion of the promissory note to
     any of the twelve (12) Federal Reserve Banks organized under Section 4 of
     the Federal Reserve Act, 12 U.S.C. Section 341. No such pledge or
     enforcement thereof shall release Bank from its obligations under any of
     the loan documents.

         (l) Borrower and any Guarantor hereby grant to Bank, a lien, security
     interest and right of setoff as security for all liabilities and
     obligations to Bank, whether now existing or hereafter arising, upon and
     against deposits, credits, collateral 
<PAGE>
 
     and property, now or hereafter in the possession, custody, safekeeping or
     control of Bank or any entity under the control of Fleet Financial Group,
     Inc., or in transit to any of them. At any time, without demand or notice,
     Bank may set off the same or any part thereof and apply the same to any
     liability or obligation of Borrower and any Guarantor even though unmatured
     and regardless of the adequacy of any other collateral securing the Loan.
     ANY AND ALL RIGHTS TO REQUIRE BANK TO EXERCISE ITS RIGHTS OR REMEDIES WITH
     RESPECT TO ANY OTHER COLLATERAL WHICH SECURES THE LOAN, PRIOR TO EXERCISING
     ITS RIGHT OF SETOFF WITH RESPECT TO SUCH DEPOSITS, CREDITS OR OTHER
     PROPERTY OF THE BORROWER OR ANY GUARANTOR, ARE HEREBY KNOWINGLY,
     VOLUNTARILY AND IRREVOCABLY WAIVED.

     6. Except as set forth on the attached Schedule A, all of the information
     set forth on the Schedules to the Loan Agreement is true and accurate as of
     the date hereof, and such Schedules are hereby incorporated herein by
     reference as if they were attached hereto.

     7. In all other respects the Loan Agreement remains unmodified and in full
     force and effect, and is hereby ratified and affirmed. Borrower represents
     and warrants to Bank that no default now exists under the Loan Agreement.
     From and after the date of this First Amendment, any reference in the Loan
     Agreement to "this Agreement" and any reference to the Loan Agreement
     between Borrower and Bank, shall mean such Agreement as amended hereby

     IN WITNESS WHEREOF, the parties hereto have caused this First Amendment to
     Loan Agreement to be duly executed as an instrument under seal by their
     respective officers thereunto duly authorized, as of the date first above
     written, regardless of the actual date of execution and delivery.



     WITNESS                                   CONTROL DEVICES, INC.
                                               
                                               
     /S/ Michael A. Foisy                      BY  /S/ Jeffrey G. Wood
     --------------------                          -------------------------

                                               Print Name    Jeffrey G. Wood   
                                                         --------------------- 
                                               Its: Vice President - CFO
                                                    --------------------------- 



                                               FLEET BANK OF MAINE


     /S/ Coustance Bilodeau                    BY: /S/ Peter Sylvestre
     -----------------------                       -------------------
                                               Peter Sylvestre
                                               Its Vice President
<PAGE>
 
                              LINE OF CREDIT NOTE
                                        
$20,000,000.00                              As of September 30, 1998

     FOR VALUE RECEIVED, the undersigned CONTROL DEVICES, INC., an Indiana
corporation ("Maker"), promises to pay to the order of FLEET BANK OF MAINE, a
Maine financial institution (together with its successors and assigns as holder
of this Note, the "Bank"), the sum of Twenty Million Dollars ($20,000,000.00),
or so much thereof as may be advanced, which Maker may borrow in full or in
part, repay in full or in part, and reborrow in accordance with the terms of a
Loan Agreement between maker and Bank, dated as of October 8, 1996, as amended
by First Amendment dated as of September 30, 1998 (the "Loan Agreement")
together with interest upon the principal sum thereof from tie to time advanced,
computed from the date of each advance at an interest rate selected by maker in
accordance with the terms of the Loan Agreement. Interest is payable as set
forth in the Loan Agreement, and the entire outstanding amount hereof is due on
September 30, 2000, or sooner if the term hereof is accelerated by Bank in
accordance with the Loan Agreement. Payments may be applied as follows, at the
option of the holder hereof: (1) first to all fees and charges payable hereunder
or in connection herewith, other than principal or interest; (2) second to the
interest on the unpaid balance of the debt evidenced hereby, with interest on
all overdue interest at the same rate and (3) the remainder to the unpaid
principal of the debt, until the same is paid in full.

     If any monthly installment of interest is not received with ten (10) days
of the date due, the maker shall be liable for a late fee of five percent (5%)
of the amount of such delinquent installment. If this Note is not paid in full
on September 30, 2000, or on such other date as may be specified in any demand
for payment made by the Bank in accordance with the terms of the Loan Agreement,
interest on the unpaid balance shall accrue at a fluctuating rate equal to five
percent (5%) per annum above the rate(s) that would otherwise apply, until paid
in full. All computation of interest due hereunder shall be based on the actual
number of days elapsed over a 360-day year.

     This Note is subject to the condition that at no time shall Maker be
obligated to required to pay interest at a rate which could subject the holder
hereof to either civil or criminal liability, forfeiture or less of principal,
interest, or other sums as a result of being in excess of the maximum interest
rate which Maker is permitted by law to contract or agree to pay or which the
holder hereof is permitted to receive. If by the terms of this Note Maker is at
any time required or obligated to pay interest at a rate in excess of such
maximum rate, the rate of interest under this Note shall be deemed to be
immediately reduced to such maximum rate for so long as such maximum rate shall
be in effect and shall thereafter by payable at the rate herein provided.

     Maker and any other party liable herefor may prepay this Note in full or in
part from time to time without premium or penalty, provided that prior written
notice of the intention to make prepayment must be given to the holder hereof
and provided further that the Yield Maintenance Formula referred to in the Loan
Agreement may be applicable to certain prepayments. Such optional prepayment
privilege is in addition to, and not in substitution of, any repayment of
principal required or otherwise contemplated under the Loan Agreement.

     Maker and all other parties liable herefor, whether principal, guarantor,
endorser or otherwise, hereby severally waive demand, presentment, protest and
notice of every kind, and waive all recourse to suretyship and guarantorship
defenses generally, including, but not limited to, any extensions of time for
payment or performance which may granted to Maker or to any other liable party,
any modification or amendments to this Note, the Loan Agreement or any documents
securing payment and performance hereof or thereof, any act or omission to act
by or on behalf of the holder hereof, any invalidity or unenforceability or any
security, guaranty or endorsement given herefor, any release of security,
whether any such release is intentional, 
<PAGE>
 
unintentional or by operation of law, and all other indulgences of any type
which may be granted by the holder hereof to Maker or to any other party liable
herefor. Maker and such other parties further severally waive any right to
indemnity, contribution, exoneration or reimbursement of any kind by any other
party directly or indirectly liable herefor, whether maker, endorser, guarantor
or otherwise, on account of any payment made hereunder, and further severally
waive any right of subrogation to the rights, remedies or security of the holder
hereof on account of any payment made hereunder, and do also agree that they are
jointly and severally liable to the holder hereof for all costs and expenses
arising out of or related to the negotiation, enforcement and/or administration
of this Note and/or the Loan Agreement, including any of the foregoing related
to the collection of the indebtedness incurred in connection therewith including
reasonable attorney's fees.

     All installments and sums due hereunder shall be paid to Fleet Bank of
Maine, as payee hereof at Two Portland Square, PO Box 1280, Portland, Maine
04104, or to such other parties or addresses as the holder hereof may from time
to time designate in writing to maker or to other parties liable herefor. This
Note evidences a loan for business and commercial purposes, and not for
personal, family, or household purposes.

     No invalidity or unenforceability or any portion of this Note shall affect
the validity or enforceability of the remaining portions hereof. This Note shall
be construed in accordance with the laws of the State of Maine as an instrument
given under seal.


ATTEST:                                 CONTROL DEVICES, INC.


                                  BY:  /S/ Jeffrey G. Wood
--------------------------             ----------------------------

                                  Print Name  Jeffrey G. Wood
                                              ---------------------

                                  Its:   Vice President CFO
                                         --------------------------