<PAGE>
                                                                     Exhibit 4.1


                      AMENDMENT NO. 1 TO RIGHTS AGREEMENT

         This Amendment (the "Amendment"), dated as of May 5, 2005, is by and
between The Lamson & Sessions Co., an Ohio corporation (the "Company"), and
National City Bank (the "Rights Agent").

                                    RECITALS

         A. The Company and the Rights Agent are currently parties to the Rights
Agreement, dated as of September 8, 1998 (the "Rights Agreement").

         B. The Company desires to amend the Rights Agreement in accordance with
Section 27 thereof.

         NOW, THEREFORE, the Company and the Rights Agent agree as follows:

1.       AMENDMENT TO RIGHTS AGREEMENT.

         The parties hereto agree that the Rights Agreement shall be amended as
provided below, effective as of the date of this Amendment:

         (a)      Subsection (a) of Section 1 of the Rights Agreement shall be
                  deleted in its entirety and replaced with the following:

                  "(a) "Acquiring Person" means any Person (other than the
                  Company or any Related Person) who or which, together with all
                  Affiliates and Associates of such Person, is the Beneficial
                  Owner of 20% or more of the then-outstanding Common Shares;
                  PROVIDED, HOWEVER, that a Person will not be deemed to have
                  become an Acquiring Person solely as a result of a reduction
                  in the number of Common Shares outstanding unless and until
                  such time as (i) such Person or any Affiliate or Associate of
                  such Person thereafter becomes the Beneficial Owner of
                  additional Common Shares representing 1% or more of the
                  then-outstanding Common Shares, other than as a result of a
                  stock dividend, stock split or similar transaction effected by
                  the Company in which all holders of Common Shares are treated
                  equally, or (ii) any other Person who is the Beneficial Owner
                  of Common Shares representing 1% or more of the
                  then-outstanding Common Shares thereafter becomes an Affiliate
                  or Associate of such Person. Notwithstanding the foregoing, if
                  the Directors of the Company determine in good faith that a
                  Person who would otherwise be an "Acquiring Person" as defined
                  pursuant to the foregoing provisions of this paragraph (a),
                  has become such inadvertently, and such Person divests as
                  promptly as practicable a sufficient number of Common Shares
                  so that such Person would no longer be an "Acquiring Person"
                  as defined pursuant to the foregoing provisions of this
                  paragraph (a), then such Person shall not be deemed to be an
                  "Acquiring Person" for any purposes of this Agreement."

         (b)      Subsection (h) of Section 1 of the Rights Agreement shall be
                  deleted in its entirety and replaced with the following:

                  "(h) "Distribution Date" means the earlier of: (i) the Close
                  of Business on the tenth calendar day following the Share
                  Acquisition Date, or (ii) the Close of Business on the tenth
                  Business Day (or, unless the Distribution Date shall have
                  previously occurred, such later date as may be specified by
                  the Directors of the Company) after the commencement of a
                  tender or exchange offer by any Person (other than the Company
                  or any Related Person), if upon the consummation thereof such
                  Person would be the Beneficial Owner of 20% or more of the
                  then-outstanding Common Shares."
<PAGE>

2.       MISCELLANEOUS.

         (a)      Except as otherwise expressly provided, or unless the context
                  otherwise requires, all capitalized terms used herein have the
                  meanings assigned to them in the Rights Agreement.

         (b)      The term "Agreement" as used in the Rights Agreement shall be
                  deemed to refer to the Rights Agreement as amended by this
                  Amendment. The Rights Agreement will not otherwise be
                  supplemented or amended by virtue of this Amendment, but shall
                  remain in full force and effect.

         (c)      Each party hereto waives any requirement under the Rights
                  Agreement that any additional notice be provided to it
                  pertaining to the matters covered by this Amendment.

         (d)      Exhibits B and C to the Rights Agreement shall be deemed
                  amended in a manner consistent with this Amendment.

         (e)      This Amendment will be deemed to be a contract made under the
                  internal substantive laws of the State of Ohio and for all
                  purposes will be governed by and construed in accordance with
                  the internal substantive laws of such State applicable to
                  contracts to be made and performed entirely within such State.

         (f)      This Amendment may be executed in any number of counterparts
                  and each of such counterparts will for all purposes be deemed
                  to be an original, and all such counterparts will together
                  constitute but one and the same instrument.

                  [REMAINDER OF PAGE INTENTIONALLY LEFT BLANK]


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         IN WITNESS WHEREOF, the parties have caused this amendment to be duly
executed and attested, all as of the day and year first written above.



<TABLE>
<CAPTION>
ATTEST:                                                       THE LAMSON & SESSIONS CO.

<S>                                                           <C>
By: /s/ Aileen Liebertz                                       By:  /s/ James J. Abel
   --------------------------------------------------            --------------------------------------------------

Name: Aileen Liebertz                                         Name: James J. Abel
     ------------------------------------------------              ------------------------------------------------

Title:  Manager, Investor Relations and                       Title: Executive Vice President, Secretary,
        Shareholder Communications                                   Treasurer and Chief Financial Officer
      -----------------------------------------------               -----------------------------------------------

<CAPTION>
ATTEST:                                                       NATIONAL CITY BANK
                                                              AS RIGHTS AGENT
<S>                                                           <C>
By: /s/ Beth A. Rudolph                                       By: /s/ Sharon R. Boughter
   --------------------------------------------------            --------------------------------------------------

Name: Beth A. Rudolph                                         Name: Sharon R. Boughter
     ------------------------------------------------              ------------------------------------------------

Title: Administrative Assistant                               Title: Assistant Vice President
      -----------------------------------------------               -----------------------------------------------
</TABLE>



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