The Pololu Universal Aluminum Mounting Hub for 1/4″ (6.35mm) Shaft, #4-40 Holes (2-Pack) facilitates the attachment of custom wheels and mechanisms to motor shafts of 0.250 inch (6.35 mm) diameter. This set includes two hubs, each featuring six threaded mounting holes for secure attachment. The hubs are compatible with both round and "D" shafts, including those on NEMA 23 stepper motors. Additionally, four #4-40 set screws and a 0.05″ Allen wrench are provided to ensure a secure fit between the shaft and hub.