These new hard plastic wheels are specially designed for our GM2, GM3, GM8, GM9 and GM17 gear motor output shafts. Although usable as wheels, we often use these as mounts for legs and other mechanisms as they have convenient mounting holes that match our leg mounting pads. They are 30mm in diameter, 7mm wide, and the double-flat slot fits onto the gear motor's shaft snuggly. Wheels are sold individually, and come with a screw and washer to secure it. Motor not included.