The set includes one Allen wrench and two 4-40 set screws for securing the hubs to motor shafts.
These universal mounting hubs are designed to work with most 4 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.