These universal aluminum mounting hubs allow you to mount custom wheels and mechanisms to 1/4 inch (6.35 mm) diameter motor shafts. The set includes two hubs, four #4-40 set screws for securing the hubs to motor shafts, and one 0.05″ Allen wrench for use with the set screws. Each hub has six threaded mounting holes for #4-40 screws (not included).