The Pololu universal aluminum mounting hub allows you to mount custom wheels and mechanisms to 6 mm motor shafts. The hubs are sold in pairs, and each hub includes two 4-40 set screws for securing a motor shaft to the hub.
These universal mounting hubs are designed to work with most 6 mm shafts, including round shafts and “D” shafts. Each hub has six mounting holes for 4-40 screws, letting you mount custom wheels or mechanisms to your motors. 4-40 hex set screws (two included for each hub) allow secure coupling of shaft to hub. The kit includs set screws and a matching 0.05" hex wrench .
Mechanical drawing for the Pololu universal aluminum mounting hub for 6 mm shaft.