Abstract: A shank for an adjustable boring bar is disclosed herein having first and second members telescopically engaged in a nonrotatable relation from one to the other with one of the members having mounted thereon an axially adjustable abutment means such that rotation of the abutment means on one member provides relative axial movement between the first and second members. A recess is shown formed on the outer surface of the innermost telescopically engaged member, the recess having a declining surface in the direction of the abutment means such that a clamp element located and engaged in the outermost telescopically engaged member is operable downwardly to engage said declining surface and hold the first and second members in a firm abutting relationship.