The Tamiya 4speed crankaxle gearbox has four possible gear ratios including the highest gear ratio of Tamiyas gearbox series 5402:1 as well as 126:1 441:1 and 1543:1. This gearbox also features a worm gear which locks the output shaft when the motor is not turning. A clutch gear prevents the gearbox from destroying itself in case the output shaft gets stuck. The kit comes with all parts necessary to build the gearbox in any of the four possible configurations.