The Pololu universal aluminum mounting hub allows you to mount custom wheels and mechanisms to 3 mm motor shafts. The hubs are sold in pairs, and each hub includes one 4-40 set screw for securing a motor shaft to the hub. The set includes one Allen wrench and two 4-40 set screws for securing the hubs to motor shafts. Each hub has four mounting holes for 4-40 screws (not included).
These universal mounting hubs are designed to work with most 3 mm shafts, including round shafts, and “D” shafts. Each hub has four mounting holes for 4-40 screws (not included), letting you mount custom wheels or mechanisms to your motors. 4-40 hex set screws (one included for each hub) allow secure coupling of shaft to hub. A 0.05″ hex wrench (often the smallest size in SAE Allen wrench sets) is included for use with the set screws.