This is a brass Universal socket for a 1/8" drive shafts or motor shafts (most .05 motors have a 1/8" shaft). It is designed to be used with a coupling rod (or "dogbone") #2019 (DUMB1620). This package has one brass Universal socket and one set screw (which uses a 1/16" hex wrench to tighten). The set screw holds the shaft to the socket. 9-16-93/eke