This is a Robinson Racing 5mm Bore, 39 Tooth, 48 Pitch Machined Pinion Gear. This pinon Can be used on any car that uses a 48 pitch spur, when using a motor that has a 5mm rotor shaft. Robinson Racing pinions are precision machined from high quality steel for durability, and have the number of teeth stamped on the side for easy identification. One 4mm set screw included.