Document:

<PAGE>

                                                                    Exhibit 4.20

                                    GUARANTY
                                    --------

This Guaranty is entered into as of May __, 2001, by the undersigned Guarantors
(each a "Guarantor") and Royal Bank of Scotland, PLC in its capacity as a
         ---------
Guaranteed Party, and Agent for itself and on behalf of National Westminster
Bank, PLC (Royal Bank of Scotland, PLC and National Westminster Bank, PLC,
sometimes collectively herein "Banks").

                                  WITNESSETH:
                                  -----------

        WHEREAS, APW Enclosure Products and Systems Limited, its subsidiaries
and affiliates, APW Limited, APW Electronics Group Plc its subsidiaries and
affiliates (collectively "Borrowers") have severally entered into various credit
facilities with the Banks including (1) Revolving Credit Facilities, as amended,
dated October 24, 1995 with Royal Bank of Scotland, PLC; (2) Counter-Indemnity
Agreement dated on or about April 26, 2000; with National Westminster Bank, PLC
and (3) a Multiline Facility Agreement dated April 20, 2000 with National
Westminster Bank, PLC pursuant to which the Banks agreed to extend financial
accommodations including loans, bills facilities, bonding facilities,
guarantees, indemnifications and related credit facilities (collectively "Credit
Facilities") for the account of its Borrowers as set forth in the respective
credit and indemnity documents.

        WHEREAS, the Banks have no obligation at the present time to make
additional loans or issue or participate in additional Credit Facilities under
various Credit Facility documents however Banks are willing to do so on the
condition (among others) that the Guarantor enter into this Guaranty.

        The Guarantor will derive substantial and direct benefits (which
benefits are hereby acknowledged by the Guarantor) from the Loans and the
financial accommodations and other benefits to be provided by Banks.

        In order to induce the Banks to make such Loans and other consideration
available to the Borrowers as provided in the Credit Facilities and to make
certain forbearances thereunder, the Guarantor has agreed to issue this
Guaranty.

        NOW, THEREFORE, for and in consideration of any forbearance, loan,
advance or other financial accommodation heretofore or hereafter made to the
Borrowers under or in connection with the Credit Facilities, and for other good
and valuable consideration, the receipt and sufficiency of which are hereby
acknowledged, the parties hereto agree as follows:

        1.  Definitions. Unless otherwise defined herein, capitalized terms used
            -----------
in this Guaranty have the meanings given to them from time to time in the Credit
Facilities. APW Limited, its subsidiaries and affiliates, APW Enclosure Products
and Systems Limited, its subsidiaries and affiliates, and APW Electronics Group
PLC its subsidiaries and affiliates are collectively called the "Guaranteed
Borrower."

        2.  Guaranty.
            --------
<PAGE>

               2.1    Guaranty. The Guarantor hereby irrevocably, absolutely and
                      --------
unconditionally guarantees the full and punctual payment or performance when
due, whether at stated maturity, by required prepayment, declaration,
acceleration, demand or otherwise, of all of the Obligations of the Guaranteed
Borrower to the Banks (the "Guaranteed Obligations"), including Obligations in
                            ----------------------
respect of amounts that would become due but for the operation of the automatic
stay under Section 362(a) of the U.S. Bankruptcy Code, the operation of Sections
502(b) and 506(b) of the U.S. Bankruptcy Code or the operation of any comparable
provisions of laws of countries other than the United States; provided, however,
that the Guarantor shall be liable under this Guaranty for the maximum amount of
--------  -------
such liability that can be hereby incurred without rendering this Guaranty, as
it relates to the Guarantor, voidable under applicable law relating to
fraudulent conveyance, fraudulent transfer or other applicable law, and not for
any greater amount. This Guaranty constitutes a guaranty of payment and
performance when due and not of collection, and the Guarantor specifically
agrees that it shall not be necessary or required that the Agent or any Bank
exercise any right, assert any claim or demand or enforce any remedy whatsoever
against the Guaranteed Borrower (or any other Person) before or as a condition
to the obligations of the Guarantor hereunder. The Agent or any Bank may permit
the indebtedness of the Guaranteed Borrower to the Agent or any Bank to include
indebtedness other than the Guaranteed Obligations, and may apply any amounts
received from any source, other than from the Guarantor, to that portion of the
Guaranteed Borrower's indebtedness to the Agent or any Bank which is not a part
of the Obligations.

               2.2    Currency. Payments hereunder shall be made in the same
                      --------
currency as the Guaranteed Obligations so guaranteed. If and to the extent
payments hereunder are made in a different currency, payments required hereunder
shall be increased to the extent necessary to avoid any loss to the Agent or the
Banks on account of any change or changes in the value of such different
currency from the currency of the applicable Guaranteed Obligations.

               2.3    Obligations Independent. The obligations hereunder are
                      -----------------------
independent of the obligations of the Guaranteed Borrower, and a separate action
or actions may be brought and prosecuted against the Guarantor whether any
action is brought against the Guaranteed Borrower or whether the Guaranteed
Borrower shall be joined in any such action or actions.

               2.4    Authorization of Renewals, Etc. The Guarantor authorizes
                      ------------------------------
the Agent and each Bank, without notice or demand and without affecting its
liability hereunder, from time to time:

                      (a)  to renew, compromise, extend, accelerate or otherwise
change the time for payments of, or otherwise change the terms of, the
Guaranteed Obligations, including increase or decrease of the rate of interest
thereon, or otherwise change the terms of the Credit Agreement or any other Loan
Document, as permitted therein;

                      (b)  to receive and hold security for the payment of this
Guaranty or the Guaranteed Obligations and exchange, enforce, waive, release,
fail to perfect, sell, or otherwise dispose of any such security;

                      (c)  to apply such security and direct the order or manner
of thereof as the Agent or any Bank, as the case may be, in its discretion may
determine, and

                                       2
<PAGE>

                  (d)   to release or substitute any one or more of any
endorsers or guarantors of the Guaranteed Obligations.

The Guarantor further agrees that the performance or occurrence of any of the
acts or events described in clauses (a), (b), (c), and (d) above with respect to
indebtedness or other obligations of the Guaranteed Borrower, other than the
Guaranteed Obligations, to the Agent or any Bank, shall not affect the liability
of the Guarantor hereunder.

          2.5     Waiver of Certain Rights. The Guarantor waives any right to
                  ------------------------
require the Agent or any Bank:

                  (a)  to proceed against the Guaranteed Borrower or any other
Person;

                  (b)  to proceed against or exhaust any security for the
Guaranteed Obligations or any other indebtedness of the Guaranteed Borrower to
the Agent or any Bank; or

                  (c)  to pursue any other remedy in the Agent's or any such
Bank's power whatsoever.

          2.6     Waiver of Certain Defenses. The Guarantor waives any defense
                  --------------------------
arising by reason of any disability or other defense of the Guaranteed Borrower
or the cessation from any cause whatsoever of the liability of the Guaranteed
Borrower, whether consensual or arising by operation of law or any bankruptcy,
insolvency or debtor relief proceeding, or from any other cause, or any claim
that the Guarantor's obligations exceed or are more burdensome than those of the
Guaranteed Borrower. The Guarantor waives all rights and defenses arising out of
an election of remedies by the Agent, or any Bank, even though that election of
remedies, such as a nonjudicial foreclosure with respect to security for the
Guaranteed Obligations, has terminated the Guarantor's rights of subrogation and
reimbursement against the Guaranteed Borrower by operation of applicable law,
and all rights or defenses the Guarantor may have by reason of protection
afforded to the Guaranteed Borrower with respect to the Guaranteed Obligations
pursuant to any antideficiency laws or other laws of applicable jurisdiction
limiting or discharging the Guaranteed Obligations. The Guarantor waives any
benefit of, and any right to participate in, any security or other guaranty now
or hereafter held by the Agent or any Bank securing the Guaranteed Obligations.

          2.7     Waiver of Presentments, Etc. The Guarantor waives all
                  ---------------------------
presentments, demands for performance, notices of nonperformance, protests,
notices of protest, notices of dishonor and notices of acceptance of this
Guaranty and of the existence or creation of new Guaranteed Obligations or any
other indebtedness of the Guaranteed Borrower to the Agent or any Bank.

          2.8     Information Relating to the Guaranteed Borrower. The
                  -----------------------------------------------
Guarantor acknowledges and agrees that it shall have the sole responsibility for
obtaining from the Guaranteed Borrower such information concerning the
Guaranteed Borrower's financial condition or business operations as the
Guarantor may require, and that neither the Agent nor any Bank has any duty at
any time to disclose to the Guarantor any information relating to the business,
operations or financial condition of the Guaranteed Borrower.

                                       3
<PAGE>

          2.9     Right of Setoff. In addition to any rights and remedies of
                  ---------------
the Banks provided by law, if the Guarantor has failed to make any payment due
hereunder upon demand, each Bank is authorized at any time and from time to
time, without prior notice to the Guarantor, any such notice being waived by the
Guarantor to the fullest extent permitted by law, to set off and apply any and
all deposits (general or special, time or demand, provisional or final)
(including deposits in other currencies in amounts determined at the Spot Rate
on the date of setoff) at any time held and other indebtedness at any time owing
by such Bank to or for the credit or the account of the Guarantor against any
and all obligations of the Guarantor now or hereafter existing under this
Guaranty or any other Loan Document, irrespective of whether or not the Agent or
such Bank shall have made demand under this Guaranty or any other Loan Document.
Each Bank agrees promptly to notify the Guarantor and the Agent after any such
set-off and application made by such Bank; provided, however, that the failure
                                           --------  -------
to give such notice shall not affect the validity of such set-off and
application. The rights of each Bank under this Section 2.9 are in addition to
                                                -----------
the other rights and remedies (including, without limitation, other rights of
set-off) which such Bank may have.

          2.10    Subordination. Any obligations of the Guaranteed Borrower to
                  -------------
the Guarantor, now or hereafter existing, constituting obligations to the
Guarantor as subrogee of the Agent or any Bank or resulting from the Guarantor's
performance under this Guaranty, are hereby fully subordinated in time and
priority of payment to the Obligations.

          2.11    Reinstatement of Guaranty. If any payment or transfer of any
                  -------------------------
interest in property by the Guaranteed Borrower to the Agent or any Bank in
fulfillment of any Guaranteed Obligation is rescinded or must at any time
(including after the return or cancellation of this Guaranty) be returned, in
whole or in part, by the Agent or any Bank to the Guaranteed Borrower or any
other Person, upon the insolvency, bankruptcy or reorganization of the
Guaranteed Borrower or otherwise, this Guaranty shall be reinstated with respect
to any such payment or transfer, regardless of any such prior return or
cancellation.

          2.12    Powers. It is not necessary for the Agent or any Bank to
                  ------
inquire into the powers of the Guaranteed Borrower or of the officers,
directors, partners or Agent acting or purporting to act on its behalf, and any
Guaranteed Obligations made or created in reliance upon the professed exercise
of such powers shall be guaranteed hereunder.

          2.13    Taxes. (a) Any and all payments by the Guarantor to each
                  -----
Bank or the Agent under this Guaranty shall be made free and clear of, and
without deduction or withholding for, any Taxes. In addition, the Guarantor
shall pay all Other Taxes.

                  (b)    If the Guarantor shall be required by law to deduct or
withhold any Taxes, Other Taxes or Further Taxes from or in respect of any sum
payable hereunder to any Bank or the Agent, then:

                         (i)     the sum payable shall be increased as necessary
     so that, after making all required deductions and withholdings (including
     deductions and withholdings applicable to additional sums payable under
     this Section), such Bank or the Agent, as the case may be, receives and
     retains an amount equal to the sum it wouId have received and retained had
     no such deductions or withholdings been made;

                                       4
<PAGE>

                         (ii)    the Guarantor shall make such deductions and
     withholdings;

                         (iii)   the Guarantor shall pay the full amount
     deducted or withheld to the relevant taxing authority or other authority in
     accordance with applicable law; and

                         (iv)    the Guarantor shall also pay to each Bank or
     the Agent for the account of such Bank, at the time interest is paid, on
     request of such Bank after such incurrence, Further Taxes in the amount
     that the respective Bank determines in good faith as necessary to preserve
     the after-tax yield such Bank would have received if such Taxes, Other
     Taxes or Further Taxes had not been imposed.

                   (c)   The Guarantor agrees to indenmify and hold harmless
each Bank and the Agent for the full amount of (i) Taxes, (ii) Other Taxes, and
(iii) Further Taxes in the amount that the respective Bank determines in good
faith as necessary to preserve the after-tax yield such Bank would have received
if such Taxes, Other Taxes or Further Taxes had not been imposed, and any
liability (including penalties, interest, additions to tax and expenses) arising
therefrom or with respect thereto, whether or not such Taxes, Other Taxes or
Further Taxes were correctly or legally asserted; provided, that the Guarantor
shall not be required to indemnify a Bank for any such liability which arose
because of the failure of said Bank to make a payment for more than five days
after such Bank became aware of the requirement to make such payment. Payment
under this indemnification shall be made within 30 days after the date the
applicable Bank or the Agent makes written demand therefor.

                   (d)   Within 30 days after the date of any payment by the
Guarantor of Taxes, Other Taxes or Further Taxes, the Guarantor shall furnish to
each Bank or the Agent the original or a certified copy of a receipt evidencing
payment thereof, or other evidence of payment satisfactory to such Bank or the
Agent.

                   (e)   For purposes of this Section, (i) "Taxes" means any and
all present or future taxes, levies, assessments, imposts, duties, deductions,
fees, withholdings or similar charges, and all liabilities with respect thereto,
excluding, in the case of each Bank and the Agent, respectively, taxes imposed
on or measured by its net income by the jurisdiction (or any political
subdivision thereof) under the laws of which such Bank or the Agent, as the case
may be, is organized or maintains a lending office in respect of the Credit
Agreement; (ii) "Other Taxes" means any present or future stamp, court or
documentary taxes or any other excise or property taxes, charges or similar
levies which arise from any payment made hereunder or from the execution,
delivery, performance, enforcement or registration of, or otherwise with respect
to, this Guaranty; and (iii) "Further Taxes" means any and all present or future
taxes, levies, assessments, imposts, duties, deductions, fees, withholdings or
similar charges (including, without limitation, net income taxes and franchise
taxes), and all liabilities with respect thereto, imposed by any jurisdiction on
account of amounts payable or paid pursuant to this Section.

     3.    Representations and Warranties. The Guarantor represents and warrants
           ------------------------------
to the Agent and each Bank as follows:

                                       5
<PAGE>

          3.1    Existence and Power. The Guarantor (a) is a corporation duly
                 -------------------
organized, validly existing and in good standing under the laws of the
jurisdiction of its incorporation; (b) has the power and authority and all
governmental licenses, authorizations, consents and approvals to own its assets,
carry on its business and to execute, deliver, and perform its obligations under
this Guaranty and any other Loan Document to which it is a party; (c) is duly
qualified as a foreign corporation, and licensed and in good standing, under the
laws of each jurisdiction where its ownership, lease or operation of property or
the conduct of its business requires such qualification or license except to the
extent failure to so qualify would not have a Material Adverse Effect; and (d)
is in compliance with all Requirements of Law except to the extent the failure
to so comply would not have a Material Adverse Effect.

          3.2    Corporate Authorization; No Contravention. The execution,
                 -----------------------------------------
delivery and performance by the Guarantor of this Guaranty and any other Loan
Document to which it is party, have been duly authorized by all necessary
corporate action, and do not and will not (a) contravene the terms of any of the
Guarantor's Organic Documents; (b) conflict with or result in any material
breach or contravention of, or the creation of any lien under, any document
evidencing any material Contractual Obligation to which the Guarantor is a party
or any order, injunction, writ or decree of any Governmental Authority to which
the Guarantor or its property is subject; or (c) violate any Requirement of Law.

          3.3    Governmental Authorization. No approval, consent, exemption,
                 --------------------------
authorization, or other action by, or notice to, or filing with, any
Governmental Authority is necessary or required in connection with the
execution, delivery or performance by, or enforcement against, the Guarantor of
this Guaranty or any other Loan Document to which it is a party.

          3.4    Binding Effect. This Guaranty and each other Loan Document to
                 --------------
which the Guarantor is a party constitute the legal, valid and binding
obligations of the Guarantor, enforceable against the Guarantor in accordance
with their respective terms, except as enforceability may be limited by
applicable bankruptcy, insolvency, or similar laws affecting the enforcement of
creditors' rights generally or by equitable principles relating to
enforceability.

          3.5    Regulated Entities. The Guarantor is not subject to any statute
                 ------------------
or regulation limiting its ability to incur or guarantee Debt.

     4.   Miscellaneous.
          -------------

          4.1 Application of Payments on Guaranty. All payments required to
              -----------------------------------
be made by the Guarantor hereunder shall, unless otherwise expressly provided
herein, be made to the Agent for the account of the Banks at the Agent's Payment
Office. The Agent will promptly distribute to each Bank its share of such
payment in like funds as received. Payments received from the Guarantor shall,
unless otherwise expressly provided herein, be applied to costs, fees, or other
expenses due under the Loan Documents, any interest, any principal due under the
Loan Documents and any other Guaranteed Obligations, in such order as the Agent,
with the consent of or at the request of the Required Banks, shall determine.

                                       6
<PAGE>

          4.2    Assignments and Participations. Any Bank may from time to
                 ------------------------------
time, without notice to the Guarantor and without affecting the Guarantor's
obligations hereunder, transfer its interest in the Guaranteed Obligations to
Participants and Assignees as provided in the Credit Agreement. The Guarantor
agrees that each such transfer will give rise to a direct obligation of the
Guarantor to each such Participant and Assignee and that each such Participant
and Assignee shall have the same rights and benefits under this Guaranty as it
would have if it were a Bank party to the Credit Agreement and this Guaranty.

          4.3    Loan Document. This Guaranty is a Loan Document executed and
                 -------------
delivered pursuant to the Credit Agreement and shall (unless otherwise expressly
indicated herein) be construed, administered and applied in accordance with the
terms and provisions thereof.

          4.4    Waivers; Writing Required. No delay or omission by the Agent
                 -------------------------
or any Bank to exercise any right under this Guaranty shall impair any such
right, nor shall it be construed to be a waiver thereof. No waiver of any single
breach or default under this Guaranty shall be deemed a waiver of any other
breach or default. Any amendment or waiver of any provision of this Guaranty
must be in writing and signed by the Guarantor and the Agent, with the written
consent of the Required Banks or all of the Banks, in accordance with the terms
of Section 10.1 of the Credit Agreement.

          4.5    Remedies. All rights and remedies provided in this Guaranty
                 --------
and any instrument or agreement referred to herein are cumulative and are not
exclusive of any rights or remedies otherwise provided by law. Any single or
partial exercise of any right or remedy shall not preclude the further exercise
thereof or the exercise of any other right or remedy.

          4.6    Costs and Expenses. The Guarantor agrees to pay or reimburse
                 ------------------
the Agent and each Bank within five Business Days after demand for all
reasonable costs and expenses (including Attorney Costs) incurred by them in
connection with the enforcement, attempted enforcement, or preservation of any
rights or remedies under this Guaranty (including in connection with any
"workout" or restructuring regarding amounts due under this Guaranty, and
including in any insolvency proceeding or appellate proceeding).

          4.7    Severability. The illegality or unenforceability of any
                 ------------
provision of this Guaranty or any instrument or agreement referred to herein
shall not in any way affect or impair the legality or enforceability of the
remaining provisions of this Guaranty or any instrument or agreement referred to
herein.

          4.8    Governing Law and Jurisdiction. (a) THIS GUARANTY SHALL BE
                 ------------------------------
GOVERNED BY, AND CONSTRUED IN ACCORDANCE WITH, THE LAW OF THE STATE OF
WISCONSIN; PROVIDED THAT THE AGENT AND THE BANKS SHALL RETAIN ALL RIGHTS ARISING
UNDER FEDERAL LAW.

                 (b)    ANY LEGAL ACTION OR PROCEEDING WITH RESPECT TO THIS
GUARANTY AND ANY OTHER LOAN DOCUMENTS MAY BE BROUGHT IN THE COURTS OF THE STATE
OF WISCONSIN OR OF THE UNITED STATES LOCATED IN WISCONSIN, AND BY EXECUTION AND
DELIVERY OF THIS GUARANTY, THE

                                       7
<PAGE>

GUARANTOR, CONSENTS, FOR ITSELF AND IN RESPECT OF ITS PROPERTY, TO THE NON-
EXCLUSIVE JURISDICTION OF THOSE COURTS. EACH OF THE GUARANTOR, THE AGENT AND THE
BANKS IRREVOCABLY WAIVES ANY OBJECTION, INCLUDING, WITHOUT LIMITATION, ANY
OBJECTION TO THE LAYING OF VENUE OR BASED ON THE GROUNDS OF FORUM NON
                                                            ---------
CONVENIENS, WHICH IT MAY NOW OR HEREAFTER HAVE TO THE BRINGING OF ANY ACTION OR
----------
PROCEEDING IN SUCH JURISDICTION IN RESPECT OF THIS GUARANTY OR ANY DOCUMENT
RELATED HERETO. THE GUARANTOR, THE AGENT AND THE BANKS EACH WAIVE PERSONAL
SERVICE OF ANY SUMMONS, COMPLAINT OR OTHER PROCESS, WHICH MAY BE MADE BY ANY
OTHER MEANS PERMITTED BY WISCONSIN LAW.

          4.9    Waiver of Jury Trial. THE GUARANTOR, THE BANKS AND THE AGENT
                 --------------------
EACH WAIVE THEIR RESPECTIVE RIGHTS TO A TRIAL BY JURY OF ANY CLAIM OR CAUSE OF
ACTION BASED UPON OR ARISING OUT OF OR RELATED TO THIS GUARANTY, THE OTHER LOAN
DOCUMENTS, OR THE TRANSACTIONS CONTEMPLATED HEREBY OR THEREBY, IN ANY ACTION,
PROCEEDING OR OTHER LITIGATION OF ANY TYPE BROUGHT BY ANY OF THE PARTIES AGAINST
ANY OTHER PARTY OR PARTIES, WHETHER WITH RESPECT TO CONTRACT CLAIMS, TORT
CLAIMS, OR OTHERWISE. THE GUARANTOR, THE BANKS AND THE AGENT EACH AGREE THAT ANY
SUCH CLAIM OR CAUSE OF ACTION SHALL BE TRIED BY A COURT TRIAL WITHOUT A JURY.
WITHOUT LIMITING THE FOREGOING, THE PARTIES FURTHER AGREE THAT THEIR RESPECTIVE
RIGHT TO A TRIAL BY JURY IS WAIVED BY OPERATION OF THIS SECTION AS TO ANY
ACTION, COUNTERCLAIM OR OTHER PROCEEDING WHICH SEEKS, IN WHOLE OR IN PART, TO
CHALLENGE THE VALIDITY OR ENFORCEABILITY OF THIS GUARANTY OR THE OTHER LOAN
DOCUMENTS OR ANY PROVISION HEREOF OR THEREOF. THIS WAIVER SHALL APPLY TO ANY
SUBSEQUENT AMENDMENTS, RENEWALS, SUPPLEMENTS OR MODIFICATIONS TO THIS GUARANTY
AND THE OTHER LOAN DOCUMENTS.

          4.10   Judgment. If, for the purposes of obtaining judgment in any
                 --------
court, it is necessary to convert a sum due hereunder in one currency into
another currency, the rate of exchange used shall be that at which in accordance
with its normal banking procedures the Agent could purchase the first currency
with such other currency on the Business Day preceding that on which final
judgment is given. The obligation of the Guarantor in respect of any such sum
due from it to the Agent hereunder shall, notwithstanding any judgment in a
currency (the "Judgment Currency") other than that in which such sum is
               -----------------
denominated in accordance with the applicable provisions of this Guaranty (the
"Agreement Currency"), be discharged only to the extent that on the Business Day
 ------------------
following receipt by the Agent of any sum adjudged to be so due in the Judgment
Currency, the Agent may in accordance with normal banking procedures purchase
the Agreement Currency with the Judgment Currency. If the amount of the
Agreement Currency so purchased is less than the sum originally due to the Agent
in the Agreement Currency, the Guarantor agrees, as a separate obligation and
notwithstanding any such judgment, to indemnify the Agent or the Person to whom
such obligation was owing against such loss.

          4.11   Entire Agreement. This Guaranty (a) integrates all the terms
                 ----------------
and conditions mentioned herein or incidental hereto, (b) supersedes all oral
negotiations and prior

                                       8
<PAGE>

writings with respect to the subject matter hereof, and (c) is intended by the
parties as the final expression of the agreement with respect to the terms and
conditions set forth in this Guaranty and any such instrument, agreement and
document and as the complete and exclusive statement of the terms agreed to by
the parties.

              [Remainder of the Page is intentionally left blank]

                                       9
<PAGE>

       IN WITNESS WHEREOF, this Agreement has been duly executed as of the day
and year first above written.

                                          APW LTD.

                                          By: /s/ James Maxwell
                                             -----------------------------
                                              James Maxwell, Assistant Treasurer

                                          APW NORTH AMERICA INC.

                                          By: /s/ James Maxwell
                                             -----------------------------
                                              James Maxwell, Treasurer

                                          APW HOLDING DENMARK APS

                                          By:_____________________________
                                              Richard Carroll

                                          By:_____________________________
                                              Jesper Bilde

                                      S-1
<PAGE>

                                     DOMESTIC SUBSIDIARIES OF APW-NA:

                                     APW ENCLOSURE SYSTEMS, INC.
                                     APW-ERIE, INC.
                                     ASPEN MOTION TECHNOLOGIES INC.
                                     CAMBRIDGE AEROFLO, INC.
                                     ELECTRONIC SOLUTIONS
                                     HSP USA INC.
                                     INNOVATIVE METAL FABRICATION, INC.
                                     McLEAN MIDWEST CORPORATION
                                     McLEAN WEST INC.
                                     METAL ARTS MANUFACTURING, INC.
                                     PRECISION FABRICATION TECHINOLOGIES,
                                     INC.
                                     RUBICON USA, INC.
                                     ZERO-EAST DIVISION, ZERO CORPORATION
                                     ZERO ENCLOSURES, INC.
                                     ZERO INTERNATIONAL, INC.

                                        By: /s/ James Maxwell
                                           -------------------------------------
                                           James Maxwell, Treasurer or Assistant
                                        Treasurer or CFO

                                     APW ENCLOSURE SYSTEMS HOLDING, INC.

                                        By: /s/ James Maxwell
                                           -------------------------------------
                                           James Maxwell, Treasurer

                                        APW ENCLOSURE SYSTEMS, LP
                                By: APW ENCLOSURE SYSTEMS HOLDING, INC.
                                its General Partner

                                        By: /s/ James Maxwell
                                           -------------------------------------
                                           James Maxwell, Treasurer

                                     DOMESTIC SUBSIDIARIES OF PARENT:

                                        APW MAYVILLE, LLC
                                        APW WRIGHT LINE LLC
                                        ASPEN POWER SYSTEMS, LLC
                                        EDER INDUSTRIES INC.
                                        VERO ELECTRONICS INC.
                                        By: /s/ James Maxwell
                                           -------------------------------------
                                        James Maxwell, Treasurer or Assistant
                                        Treasurer

                                      S-1<PAGE>

                                                                    Exhibit 4.21

                        ASSIGNMENT OF SECURITY INTEREST
                    IN UNITED STATES TRADEMARKS AND PATENTS
                    ---------------------------------------

        FOR GOOD AND VALUABLE CONSIDERATION, receipt and sufficiency of which
are hereby acknowledged, APW LTD., a Bermuda corporation (the "Parent"), APW
NORTH AMERICA, INC., a Delaware corporation ("APW-NA"), the other persons or
entities which are listed on the signature pages hereof as assignors or which
from time to time become parties hereto as assignor (collectively, including the
Parent and APW-NA, the "Assignors" and individually each a "Assignor"), hereby
assign and grant to Royal Bank of Scotland, PLC for itself and as Agent for
National Westminster Bank, PLC (the "Assignee"), a security interest in (i) all
of the Assignors' right, title and interest in and to the United States
trademarks, trademark registrations and trademark applications (the "Marks") set
forth on Schedule A attached hereto, (ii) all of the Assignors' right, title and
interest in and to the United States patents and patent applications (the
"Patents") set forth on Schedule B attached, in each case together with (iii)
all Proceeds (as such term is defined in the Security Agreement referred to
below) and products of the Marks and Patents, (iv) the goodwill of the
businesses with which the Marks are associated and (v) all causes of action
arising prior to or after the date hereof for infringement of any of the Marks
and Patents or unfair competition regarding the same. It is acknowledged by
Assignee that this assignment is subordinate to any prior validly perfected
assignment in favor of Bank of America National Association or Administrative
Agent for certain Banks under a Multi Currency Credit Agreement dated as of July
31, 2000.

       THIS ASSIGNMENT is made to secure the satisfactory performance and
payment of all the Obligations of each of the Assignors, pursuant to the
Security

                                       1
<PAGE>

Agreement among the Assignors, the other assignors from time to time party
thereto and the Assignee, dated as of March 30, 2001 (as amended from time to
time, the "Security Agreement"). Upon the payment in full of all Liabilities and
the termination of all Commitments, the Assignee shall, upon such satisfaction,
execute, acknowledge, and deliver to the Assignors an instrument in writing
releasing the security interest in the Marks and Patents acquired under this
Assignment.

       This Assignment has been granted in conjunction with the security
                       ---
interest granted to the Assignee under the Security Agreement. The rights and
remedies of the Assignee with respect to the security interest granted herein
are without prejudice to, and are in addition to those set forth in the Security
Agreement, all terms and provisions of which are incorporated herein by
reference. In the event that any provisions of this Assignment are deemed to
conflict with the Security Agreement, the provisions of the Security Agreement
shall govern. Capitalized terms that are not otherwise defined herein shall have
the respective meanings assigned thereto in the Security Agreement.

                                       2
<PAGE>

       IN WITNESS WHEREOF, the undersigned have executed this assignment as of
the___ day of May, 2001.

                                            APW LTD.

                                             /s/ James Maxwell
                                            -------------------------------
                                            By: James Maxwell
                                            Title: Assistant Treasurer

                                            DOMESTIC SUBSIDIARIES OF
                                            PARENT:

                                            APW MAY VILLE, LLC
                                            APW WRIGHT LINE LLC
                                            ASPEN POWER SYSTEMS, LLC
                                            EDER INDUSTRIES INC.
                                            VERO ELECTRONICS INC.

                                             /s/ James Maxwell
                                            -------------------------------
                                            By: James Maxwell
                                            Title: Treasurer or Assistant
                                            Treasurer, as applicable

                                       3
<PAGE>

                                            APW NORTH AMERICA INC.

                                            /s/ James Maxwell
                                            ---------------------------------
                                            By: James Maxwell
                                            Title: Treasurer

                                            DOMESTIC SUBSIDIARIES OF APW-
                                            NA:

                                            APW ENCLOSURE SYSTEMS, INC.
                                            APW-ERIE, INC.
                                            ASPEN MOTION TECHNOLOGIES INC.
                                            CAMBRIDGE AEROFLO, INC.
                                            ELECTRONIC SOLUTIONS
                                            HSP USA INC.
                                            INNOVATIVE METAL FABRICATION, INC.
                                            MCCLEAN MIDWEST CORPORATION
                                            MCCLEAN WEST INC.
                                            METAL ARTS MANUFACTURING, INC.
                                            PRECISION FABRICATION
                                            TECHNOLOGIES, INC.
                                            RUBICON USA INC.
                                            ZERO-EAST DIVISION,
                                            ZERO CORPORATION
                                            ZERO ENCLOSURES, INC.
                                            ZERO INTERNATIONAL, INC.

                                            /s/ James Maxwell
                                            ---------------------------------
                                            By: James Maxwell
                                            Title: Treasurer, Assistant
                                            Treasurer or Chief Financial
                                            Officer, as applicable

                                       4
<PAGE>

                                            APW ENCLOSURE SYSTEMS
                                            HOLDING, INC.

                                            /s/ James Maxwell
                                            ---------------------------------
                                            By:  James Maxwell
                                            Title: Treasurer

                                            APW ENCLOSURE SYSTEMS, LP by
                                            APW ENCLOSURE SYSTEMS
                                            HOLDING, INC., its General Partner

                                            /s/ James Maxwell
                                            ---------------------------------
                                            By:  James Maxwell
                                            Title: Treasurer

                                       5
<PAGE>

                                            ROYAL BANK OF SCOTLAND, PLC

                                            By:__________________________
                                            Title:

                                       6
<PAGE>

STATE OF ____________________)
                             )ss.:
COUNTY OF ___________________)

       On this___ day of May, 2001, before me personally came James Maxwell who,

being by me duly sworn, did state as follows: that he is Treasurer, Assistant

Treasurer or Chief Financial Officer of: APW LTD.; APW MAYVILLE, LLC; APW WRIGHT

LINE LLC; ASPEN POWER SYSTEMS, LLC; EDER INDUSTRIES INC.; VERO ELECTRONICS INC.;

APW NORTH AMERICA INC.; APW ENCLOSURE SYSTEMS, INC.; APW-ERIE, INC.; ASPEN

MOTION TECHNOLOGIES INC.; CAMBRIDGE AEROFLO, INC.; ELECTRONIC SOLUTIONS; HSP USA

INC.; INNOVATIVE METAL FABRICATION, INC.; MCCLEAN MIDWEST CORPORATION; MCCLEAN

WEST INC.; METAL ARTS MANUFACTURING, INC.; PRECISION FABRICATION TECHNOLOGIES,

INC.; RUBICON USA INC.; ZERO-EAST DIVISION, ZERO CORPORATION; ZERO ENCLOSURES,

INC.; and ZERO INTERNATIONAL, INC., that he is authorized to execute the

foregoing Assignment on behalf of said corporation or limited liability company

and that he did so by authority of the Board of Directors of said corporation or

limited liability company.

                                            _________________________________
                                            Notary Public

                                       7
<PAGE>

STATE OF _______________________)
                                )ss.:
COUNTY OF_______________________)

       On this ____day of May, 2001, before me personally came Howard Lederman
who, being by me duly sworn, did state as follows: that he is Vice President of
APW ENCLOSURE SYSTEMS HOLDING, INC., that he is authorized to execute the
foregoing Assignment on behalf of said corporation and that he did so by
authority of the Board of Directors of said corporation.

                                            ________________________________
                                            Notary Public

                                       8

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