Exhibit 4.1


 


	NUMBER	UNITS 


U-


SEE REVERSE FOR CERTAIN DEFINITIONS


 


CUSIP 05602L203 


 


B. RILEY PRINCIPAL 250 MERGER CORP. 


UNITS CONSISTING OF ONE SHARE OF COMMON
STOCK AND ONE-THIRD OF ONE REDEEMABLE WARRANT,

EACH WHOLE WARRANT ENTITLING THE HOLDER TO PURCHASE ONE SHARE OF COMMON STOCK


 


THIS CERTIFIES THAT is the owner of Units.


 


Each Unit (“Unit”)
consists of one (1) share of Class A common stock, par value $0.0001 per share (“Common Stock”), of B.
Riley Principal 250 Merger Corp., a Delaware corporation (the “Company”), and one-third of one redeemable
warrant (the “Warrant”). Each whole Warrant entitles the holder to purchase one share of Common Stock
for $11.50 per share (subject to adjustment). Only whole Warrants are exercisable. Each whole Warrant will become exercisable  thirty (30) days after the Company’s completion of a merger, capital stock exchange, asset acquisition,
stock purchase, reorganization or other similar business combination with one or more businesses (each a “Business
Combination”), and will
expire unless exercised before 5:00 p.m., New York City Time, on the date that is five (5) years after the date on which the Company
completes its initial Business Combination, or earlier upon redemption or liquidation (the “Expiration Date”).
The Common Stock and Warrants comprising the Units represented by this certificate are not transferable separately prior to , 2021,
unless B. Riley Securities, Inc. elects to allow separate trading earlier, subject to the Company’s filing of a Current Report
on Form 8-K with the Securities and Exchange Commission containing an audited balance sheet reflecting the Company’s receipt
of the gross proceeds of the Company’s initial public offering and filing a Current Report on Form 8-K and issuing a press
release announcing when separate trading will begin. No fractional Warrants will be issued upon separation of the Units. The terms
of the Warrants are governed by a Warrant Agreement, dated as of , 2021, between the Company and Continental Stock Transfer &
Trust Company, as Warrant Agent, and are subject to the terms and provisions contained therein, all of which terms and provisions
the holder of this certificate consents to by acceptance hereof. Copies of the Warrant Agreement are on file at the office of the
Warrant Agent at 1 State Street, 30th Floor, New York, New York 10004, and are available to any Warrant holder on written
request and without cost.


 


This certificate is not valid unless countersigned
by the Transfer Agent and registered by the Registrar of the Company.


 


This certificate shall be governed by and
construed in accordance with the internal laws of the State of New York.


 


Witness the facsimile signature of a duly
authorized signatory of the Company.


 


	 	 	 
	Authorized Signatory	 	Transfer Agent


 






     


     


    

 


B. RILEY PRINCIPAL 250 MERGER CORP. 


 


The Company will furnish
without charge to each unitholder who so requests, a statement of the powers, designations, preferences and relative, participating,
optional or other special rights of each class of equity or series thereof of the Company and the qualifications, limitations,
or restrictions of such preferences and/or rights.


 


The following abbreviations,
when used in the inscription on the face of this certificate, shall be construed as though they were written out in full according
to applicable laws or regulations:


 


	TEN COM	—	as tenants in common	UNIF GIFT MIN ACT	—	 	Custodian	 
	TEN ENT	—	as tenants by the entireties	 	 	(Cust)	 	(Minor)





	JT TEN	—	as joint tenants with right of survivorship and not as tenants in common	 	 	
        under Uniform Gifts to Minors Act

        (State)



 


Additional abbreviations
may also be used though not in the above list.


 


For value received, hereby sell, assign and transfer unto



 


(PLEASE INSERT SOCIAL SECURITY OR OTHER
IDENTIFYING NUMBER OF ASSIGNEE)


 


(PLEASE PRINT OR TYPEWRITE NAME AND ADDRESS,
INCLUDING ZIP CODE, OF ASSIGNEE)


 


Units represented by the within Certificate,
and do hereby irrevocably constitute and appoint


 


Attorney to transfer
the said Units on the books of the within named Company with full power of substitution in the premises.


Dated:


 


	 	 
	 	Notice: The signature(s) to this assignment must correspond with the name as written upon the face of the certificate in every particular, without alteration or enlargement or any change whatever.


 


Signature(s) Guaranteed:


	 	 
	THE SIGNATURE(S) MUST BE GUARANTEED BY AN ELIGIBLE GUARANTOR INSTITUTION (BANKS, STOCKBROKERS, SAVINGS AND LOAN ASSOCIATIONS AND CREDIT UNIONS WITH MEMBERSHIP IN AN APPROVED SIGNATURE GUARANTEE MEDALLION PROGRAM, PURSUANT TO S.E.C. RULE 17Ad-15 UNDER THE SECURITIES EXCHANGE ACT OF 1934, AS AMENDED (OR ANY SUCCESSOR RULE).	 


 


As more fully
described in, and subject to the terms and conditions described in, the Company’s final prospectus for its initial public
offering dated , 2021, the holder(s) of this certificate shall be entitled to receive a pro rata portion of certain funds held
in the trust account established in connection with the Company’s initial public offering only in the event that (i) the
Company redeems the shares of Common Stock sold in the Company’s initial public offering and liquidates because it does not
consummate an initial business combination by the date set forth (the “Last Date”) in the Company’s
Amended and Restated Certificate of Incorporation, as the same may be amended from time to time (the “Charter”),
(ii) the Company redeems the shares of Common Stock sold in its initial public offering properly submitted in connection with a
stockholder vote to amend the Charter to modify the substance or timing of the Company’s obligation to redeem 100% of the
Common Stock if it does not consummate an initial business combination by the Last Date, or (iii) if the holder(s) seek(s) to redeem
for cash his, her or its respective shares of Common Stock in connection with a tender offer (or proxy solicitation, solely in
the event the Company seeks stockholder approval of the proposed initial business combination) setting forth the details of a proposed
initial business combination. In no other circumstances shall the holder(s) have any right or interest of any kind in or to the
trust account.