Exhibit 4.3

                                 HSB GROUP, INC.

7.0% Convertible Subordinated Deferrable Interest Debentures due December 31,
2017

THE CONVERTIBLE SUBORDINATED INTEREST DEFERRABLE DEBENTURES EVIDENCED HEREBY AND
THE COMMON STOCK ISSUABLE UPON THEIR  CONVERSION HAVE NOT BEEN REGISTERED  UNDER
THE U.S.  SECURITIES ACT OF 1933, AS AMENDED (THE "SECURITIES ACT"), AND MAY NOT
BE OFFERED,  SOLD,  PLEDGED OR OTHERWISE  TRANSFERRED EXCEPT IN WHOLE OR IN PART
(BUT IF IN PART, IN AMOUNTS NOT LESS THAN  $10,000,000 IN PRINCIPAL  AMOUNT) AND
ONLY IN COMPLIANCE WITH THE REQUIREMENTS OF THE U.S.  SECURITIES ACT OF 1933, AS
AMENDED, OR PURSUANT TO AN APPLICABLE EXCEMPTION THEREFROM.


No. R-1                                                            $309,300,000

HSB  GROUP,   INC.,   a   Connecticut   corporation   (hereinafter   called  the
"Corporation",  which term  includes any  successor  Person under the  Indenture
hereinafter  referred  to), for value  received,  hereby  promises to pay to The
First  National  Bank of  Chicago,  as Property  Trustee,  pursuant to the Trust
Agreement  of HSB  Capital II,  dated as of December  31,  1997,  or  registered
assigns,  the principal sum of Three Hundred Nine Million Three Hundred Thousand
($309,300,000)  Dollars on December 31, 2017;  provided that the Corporation may
shorten the Stated  Maturity  of the  principal  of this  Security to a date not
earlier  than  December 31, 2012 in the  circumstances  described on the reverse
hereof.  The Corporation  further promises to pay interest on said principal sum
from  December 31, 1997 or from the most recent  Interest  Payment Date to which
interest has been paid or duly provided for,  semi-annually (subject to deferral
as set  forth  herein)  in  arrears  on  January  15 and  July 15 of each  year,
commencing  January  15,  1998,  at the rate of 7.0% per  annum,  together  with
Additional  Sums, if any, as provided in Section 10.6 of the Indenture until the
principal hereof is paid or duly provided for or made available for payment. The
amount of interest payable for any period less than a full interest period shall
be  computed  on the basis of a 360-day  year of twelve  30-day  months  and the
actual days elapsed in a partial  month in such  period.  The amount of interest
payable  for any  full  interest  period  shall  be  computed  by  dividing  the
applicable  rate per annum by two. The interest so payable,  and punctually paid
or duly  provided  for, on any Interest  Payment  Date will,  as provided in the
Indenture,  be paid to the  Person in whose name this  Security  (or one or more
Predecessor  Securities)  is  registered at the close of business on the Regular
Record Date for such interest installment,  which shall be the January 1 or July
1 (whether  or not a Business  Day),  as the case may be,  next  preceding  such
Interest Payment Date. Any such interest not so punctually paid or duly provided
for shall  forthwith  cease to be payable to the Holder on such  Regular  Record
Date and may either be paid to the Person in whose name this Security (or one or
more Predecessor Securities) is registered at the close of business on a Special
Record  Date  for the  payment  of such  Defaulted  Interest  to be fixed by the
Trustee, notice whereof shall be given to Holders of Securities not less than 10
days  prior to such  Special  Record  Date,  or be paid at any time in any other
lawful manner not inconsistent with the requirements of any securities  exchange
on which the Security may be listed,  and upon such notice as may be required by
such exchange, all as more fully provided in said Indenture.

So long as no Event of Default has occurred and is continuing,  the  Corporation
shall have the right, at any time during the term of this Security, from time to
time to defer the payment of interest on this Security for up to ten consecutive
semi-annual  interest payment periods with respect to each deferral period (each
an "Extension  Period"),  during which Extension  Periods the Corporation  shall
have the right to make  partial  payments of interest  on any  Interest  Payment
Date,  and at the end of which  the  Corporation  shall  pay all  interest  then
accrued and unpaid;  provided,  however,  that no Extension  Period shall extend
beyond the Stated  Maturity of the principal of this Security as then in effect,
and no such  Extension  Period may end on a date other than an Interest  Payment
Date; and provided further,  however, that during any such Extension Period, the
Corporation  shall not (i) declare or pay any dividends or distributions  on, or
redeem, purchase,  acquire or make a liquidation payment with respect to, any of
the  Corporation's  capital  stock,  or (ii) make any payment of principal of or
interest  or  premium,  if any,  on or  repay,  repurchase  or  redeem  any debt
securities  of the  Corporation  that rank pari  passu in all  respects  with or
junior in interest to this  Security or (iii) make any  guarantee  payments with
respect  to any  guarantee  by the  Corporation  of the debt  securities  of any
subsidiary of the  Corporation if such guarantee ranks pari passu with or junior
in interest to the  Securities  (other than (a)  dividends or  distributions  in
common stock of the Corporation, (b) any declaration of a dividend in connection
with the implementation of a stockholders' rights plan, or the issuance of stock
under any such plan in the future,  or the  redemption or repurchase of any such
rights pursuant  thereto,  (c) payments under the Guarantee and (d) purchases of
common stock  related to the issuance of common stock or rights under any of the
Corporation's or its subsidiaries'  benefit plans for their directors,  officers
or  employees).  Prior to the  termination  of any such  Extension  Period,  the
Corporation  may  further  defer  the  payment  of  interest,  provided  that no
Extension  Period  shall exceed ten  consecutive  semi-annual  interest  payment
periods,  and shall not extend  beyond the Stated  Maturity of the  principal of
this  Security or end on a date other than an Interest  Payment  Date.  Upon the
termination of any such Extension Period and upon the payment of all accrued and
unpaid interest then due on any Interest Payment Date, the Corporation may elect
to  begin  a  new  Extension  Period,  subject  to  the  above  conditions.  The
Corporation shall give the Holder of this Security and the Trustee notice of its
election to begin any  Extension  Period at least one  Business Day prior to the
next succeeding  Interest  Payment Date on which interest on this Security would
be payable but for such deferral or so long as such  Securities  are held by HSB
Capital  II, at least one  Business  Day  prior to the  earlier  of (i) the next
succeeding date on which  Distributions on the Capital Securities of such Issuer
Trust  would be payable  but for such  deferral,  and (ii) the date on which the
Property  Trustee of such Issuer  Trust is required to give notice to holders of
such Capital  Securities of the record date or the date such  Distributions  are
payable.

         Payment of the principal of (and premium,  if any) and interest on this
Security will be made at the office or agency of the Corporation  maintained for
that  purpose  in New  York,  New York or  Chicago,  Illinois,  in such  coin or
currency  of the  United  States of  America  as at the time of payment is legal
tender for payment of public and private debts;  provided,  however, that at the
option of the Corporation payment of interest may be made (i) by check mailed to
the address of the Person  entitled  thereto as such address shall appear in the
Securities Register,  or (ii) by wire transfer in immediately available funds at
such place and to such  account  as may be  designated  by the  Person  entitled
thereto as specified in the Securities Register.

         The indebtedness  evidenced by this Security is, to the extent provided
in the  Indenture,  subordinate  and  junior  in right of  payment  to the prior
payment in full of all Senior Indebtedness, and ranks pari passu with HSB Group,
Inc.'s Global Floating Rate Junior Subordinated  Debentures,  Series B, and this
Security is issued  subject to the  provisions  of the  Indenture  with  respect
thereto.  Each Holder of this Security, by accepting the same, (a) agrees to and
shall be bound by such  provisions,  (b)  authorizes  and directs the Trustee on
such Holder's  behalf to take such actions as may be necessary or appropriate to
effectuate the  subordination  so provided,  and (c) appoints the Trustee his or
her attorney-in-fact for any and all such purposes.  Each Holder hereof, by such
Holder's  acceptance  hereof,  waives  all  notice  of  the  acceptance  of  the
subordination provisions contained herein and in the Indenture by each holder of
Senior Indebtedness,  whether now outstanding or hereafter incurred,  and waives
reliance by each such holder upon said provisions.

         Reference is hereby made to the further provisions of this Security set
forth on the reverse  hereof,  which further  provisions  shall for all purposes
have the same effect as if set forth at this place.

         Unless the  certificate of  authentication  hereon has been executed by
the Trustee referred to on the reverse hereof by manual signature, this Security
shall  not be  entitled  to any  benefit  under  the  Indenture  or be  valid or
obligatory for any purpose.



         IN WITNESS  WHEREOF,  the  Corporation has caused this instrument to be
duly executed under its corporate seal.

                                             HSB GROUP, INC.


                                             By:        /s/ Saul L. Basch
                                             Name:      Saul L. Basch
                                             Title:     Senior Vice President,
                                                        Treasurer and Chief
                                                        Financial Officer

Attest:

/s/ Roberta A. O'Brien
Assistant Corporate Secretary

         SECTION 2.3.  Form of Reverse of Security.

         This  Security  is  a  duly  authorized  issue  of  securities  of  the
Corporation  (herein called the  "Securities"),  limited in aggregate  principal
amount to  $309,300,000,  issued under the  Indenture,  dated as of December 31,
1997 (herein  called the  "Indenture"),  between the  Corporation  and The First
National Bank of Chicago,  as Trustee  (herein called the "Trustee",  which term
includes any successor trustee under the Indenture),  to which Indenture and all
indentures  supplemental thereto reference is hereby made for a statement of the
respective rights,  limitations of rights,  duties and immunities  thereunder of
the Corporation, the Trustee, the holders of Senior Indebtedness and the Holders
of the  Securities,  and of the terms upon which the Securities  are, and are to
be, authenticated and delivered.

         All terms used in this Security that are defined in the Indenture or in
the Trust  Agreement,  dated as of December  31, 1997 (as  modified,  amended or
supplemented from time to time, the "Trust Agreement"),  relating to HSB Capital
II (the "Issuer Trust") among the Corporation,  as Depositor, the Trustees named
therein  and the  Holders  from  time to time  of the  Trust  Securities  issued
pursuant  thereto,  shall have the meanings assigned to them in the Indenture or
the Trust Agreement, as the case may be.

         The  Corporation  may  at any  time,  at its  option,  (i) on or  after
December 31, 2004 or (ii) for a reason specified in Article XI of the Indenture,
in  both  cases  subject  to the  terms  and  conditions  of  Article  XI of the
Indenture,  redeem  this  Security  in whole at any time or in part from time to
time  at a  Redemption  Price  equal  to 100% of the  principal  amount  hereof,
together,  in the case of any such  redemption,  with  accrued  interest  to but
excluding the Redemption Date fixed for redemption.

         Under limited circumstances,  Employers Reinsurance Corporation may, at
its  option  and  subject  to the  terms and  conditions  of  Article  XI of the
Indenture,  require  the  Corporation  to redeem this  Security  in whole,  at a
Redemption Price as stated in Section 11.8 of the Indenture.

         In addition,  upon the occurrence and during the  continuation of a Tax
Event in respect of the Issuer Trust, the Corporation may, at its option, at any
time within 90 days of the  occurrence and during the  continuation  of such Tax
Event, redeem this Security,  in whole but not in part, subject to the terms and
conditions of Article XI of the Indenture,  at a Redemption  Price equal to 100%
of the principal amount of the 7.0% Convertible Subordinated Deferrable Interest
Debentures so redeemed plus accrued and unpaid  interest  thereon to the date of
redemption.

         In the  event  of  redemption  of this  Security  in part  only,  a new
Security or Securities for the  unredeemed  portion hereof will be issued in the
name of the Holder hereof upon the cancellation hereof.

         The Indenture contains provisions for satisfaction and discharge of the
entire  indebtedness of this Security upon  compliance by the  Corporation  with
certain conditions set forth in the Indenture.

         The Indenture permits, with certain exceptions as therein provided, the
Corporation  and the Trustee at any time to enter into a supplemental  indenture
or  indentures  for the  purpose  of  modifying  in any  manner  the  rights and
obligations of the Corporation  and of the Holders of the  Securities,  with the
consent of the  Holders of not less than a majority in  principal  amount of the
Outstanding  Securities  to be  affected  by such  supplemental  indenture.  The
Indenture also contains provisions  permitting Holders of specified  percentages
in principal amount of the Securities at the time Outstanding,  on behalf of the
Holders of all Securities,  to waive  compliance by the Corporation with certain
provisions of the  Indenture  and certain past defaults  under the Indenture and
their  consequences.  Any such consent or waiver by the Holder of this  Security
shall be conclusive  and binding upon such Holder and upon all future Holders of
this  Security  and of any  Security  issued upon the  registration  of transfer
hereof or in exchange hereof or in lieu hereof,  whether or not notation of such
consent or waiver is made upon this Security.

     As provided in and subject to the provisions of the Indenture,  if an Event
of Default with respect to the Securities at the time Outstanding  occurs and is
continuing,  then and in every such case the  Trustee or the Holders of not less
than 25% in aggregate principal amount of the Outstanding Securities may declare
the  principal  amount of all the  Outstanding  Securities to be due and payable
immediately,  by a notice in writing to the  Corporation  (and to the Trustee if
given by Holders),  provided  that, if upon an Event of Default,  the Trustee or
such Holders fail to declare the principal of all the Outstanding  Securities to
be  immediately  due and  payable,  the  holders  of at least  25% in  aggregate
Liquidation  Amount of the Capital  Securities then  Outstanding  shall have the
right to make such declaration by a notice in writing to the Corporation and the
Trustee; and upon any such declaration the principal of and the accrued interest
on all the Securities  shall become  immediately due and payable,  provided that
the payment of such  principal  and  interest on such  Securities  shall  remain
subordinated to the extent provided in Article XII of the Indenture.

         Subject to the terms and  conditions  set forth in Article  XIII of the
Indenture,  this  Security is  convertible,  at the option of the  Holder,  into
shares of Common Stock.

         No reference  herein to the Indenture and no provision of this Security
or of the Indenture  shall alter or impair the  obligation  of the  Corporation,
which is absolute and  unconditional,  to pay the principal of (and premium,  if
any) and interest on this Security at the times, place and rate, and in the coin
or currency, herein prescribed.

         As provided in the Indenture and subject to certain limitations therein
set forth,  the  transfer of this  Security  is  registrable  in the  Securities
Register,  upon surrender of this Security for  registration  of transfer at the
office  or  agency  of the  Corporation  maintained  under  Section  10.2 of the
Indenture  for such  purpose,  duly  endorsed  by, or  accompanied  by a written
instrument  of  transfer  in  form  satisfactory  to  the  Corporation  and  the
Securities  Registrar  duly  executed  by,  the Holder  hereof or such  Holder's
attorney duly  authorized in writing,  and thereupon one or more new Securities,
of like tenor, of authorized  denominations and for the same aggregate principal
amount, will be issued to the designated transferee or transferees.

         The Securities are issuable only in registered  form without coupons in
denominations  of  $10,000,000  and any integral  multiple of $100,000 in excess
thereof. As provided in the Indenture and subject to certain limitations therein
set forth,  Securities are exchangeable for a like aggregate principal amount of
Securities  and  of  like  tenor  of a  different  authorized  denomination,  as
requested by the Holder surrendering the same.

         No service charge shall be made for any such  registration  of transfer
or exchange,  but the  Corporation  may require  payment of a sum  sufficient to
cover any tax or other governmental charge payable in connection therewith.

         Prior to due presentment of this Security for registration of transfer,
the Corporation, the Trustee and any agent of the Corporation or the Trustee may
treat the Person in whose name this  Security is  registered as the owner hereof
for all  purposes,  whether or not this  Security  be  overdue,  and neither the
Corporation,  the  Trustee nor any such agent shall be affected by notice to the
contrary.

         The Corporation and, by its acceptance of this Security or a beneficial
interest  therein,  the Holder of, and any  Person  that  acquires a  beneficial
interest in, this Security agree that for United States Federal, state and local
tax purposes it is intended that this Security constitute indebtedness.

         THIS SECURITY SHALL BE GOVERNED BY AND CONSTRUED IN ACCORDANCE WITH THE
LAWS OF THE STATE OF NEW YORK.

The Trustee's certificates of authentication shall be in substantially the
following form:

This is one of the Securities referred to in the within-mentioned Indenture.

Dated:  December 31, 1997

THE FIRST NATIONAL BANK OF CHICAGO
as Trustee



By: /s/ Steve M. Husbands
Authorized Officer