This is the Team Associated RC10B5M "3 Gear" Gear Box. The B5M 3-gear transmission provides the spec class racer with a lightweight/low rotating mass option to improve drivetrain efficiency. It also features a smaller, lightweight top shaft which uses smaller diameter 5x10x4mm bearings for additional weight savings. The 3-gear transmission is also a great tuning aid for modified class racing on high-grip tracks because the gyroscopic effect of the motor is reversed, helping the car stay flatter in the corners. Part# 91607