This is the optional forward only conversion kit for the Traxxas Revo(Nitro). The forward only conversion kit makes Revo legal for racing where reverse is not allowed. It reduces the internal rotating mass in the transmission for quicker acceleration and provides a small, additional weight reduction by eliminating the OptiDrive module, and the micro servo and linkage. If you are racing the Revo monster truck, this is a must have hop-up!