It has two sets of mounting holes, so it can be attached to 36mm planetary gearboxes or mounted directly to the motor. It is also compatible with the gearbox end of the following DC motors:
3265/3265E - 12V/0.5Kg-cm/670RPM 3.7:1 DC Gear Motor
3266/3266E - 12V/1.9Kg-cm/175RPM 14:1 DC Gear Motor
3267/3267E - 12V/6.6Kg-cm/49RPM 51:1 DC Gear Motor
3268/3268E - 12V/17.3Kg-cm/18RPM 139:1 DC Gear Motor