Extra hard high carbon motor pinions are built to last with our hi-performance GEN3 steel slipper units. Made from high carbon steel and then heat treated to increase the hardness of the surface even more. High carbon steel is naturally higher in lubricity and lower in adhesion than milder grades of steel making these gears ideal for use with metal spur gears. All pinions precision machined and stamped with the number of teeth. One 4mm set screw included. 2mm allen wrench (NOT INCLUDED) fits the 4mm set screw. Can be run on motors using a 5mm motor shaft including Traxxas, Associated, and HPI models or for any heavy duty application.