This is a Team Integy 38-Tooth Steel Spur Gear for the Traxxas Revo 2.5 and 3.3 trucks. A higher number of teeth on the spur gear will give you more acceleration, while a lower number of teeth will give you more top-end speed.
Two-piece construction with steel outer section and aluminum center
Team Integy 38 Tooth Steel Spur Gear for the Traxxas Revo
Installing on Revo