This gear smoothly presses onto the knurled shaft of a 9015 motor attaching to the shaft with only the friction press fit. No set screw, machine key, or collar clamp is needed. It is a slip fit (and thus will not work) on smooth shafts like the one on the Banebots 550 motor. This gear can be used for the the pinion gear in the PG27 gearboxes if switching the motor to a 9015.