This is a stock replacement part for the Traxxas Nitro Rustler (not the electric version). Features: Steel top gear shaft with preinstalled 16 tooth 32 pitch top gear. The top gear is the only gear in the transmission driven directly by the spur gear. This is done through the top gear shaft which sticks out of the side of the transmission so that the spur gear can be mounted on it. Inside the transmission, the top gear drives the larger Idler gear which,in turn, spins the differential gear. Includes: (1) Top gear shaft with top gear installed.