An adjustable shim includes a first member having a fastener opening for attachment by a screw to a frame, and a protrusion defining a coaxial threaded opening spaced from the fastener opening. A second member has a protrusion telescopically mounted on the first member and has a hollow bolt threadably located in the threaded opening coaxial with the fastener opening. The head of the hollow bolt is accessible through the second member protrusion, so that a screw can pass through the bolt to the fastener opening, and the head of the bolt is restrained from axial movement relative to the second member, so that rotation of the bolt causes the first and second members to move telescopically.