These universal mounting hubs are designed to work with most 4 mm diameter shafts, including round shafts, and “D” shafts. Each of the two included hubs has four mounting holes for #4-40 screws (not included), letting you mount custom wheels or mechanisms to your motors. The two included #4-40 hex set screws (one for each hub) allow secure coupling of shaft to hub, and a 0.05″ hex wrench (often the smallest size in SAE Allen wrench sets) is included for use with the set screws. A dimension diagram of the hub is available under the resources tab.
The picture to the right shows a hub with Pololu’s 25:1 metal gearmotor 20Dx44L mm and a Pololu 20D mm metal gearmotor bracket. These hubs will work with any Pololu 20D mm metal gearmotor or 25D mm metal gearmotor, and they also work with 60 mm, 70 mm, 80 mm, and 90 mm Pololu wheels.