This planetary gear reduction unit is designed for slowing down the motors when torque is needed more than speed. It fits 540 motor and 1: 10 RC car.Features:Perfect for 540 motor.Slow down motors when torque is needed more than speed.Sensitive in power distribution.Provide smooth vehicles starting.Prevent car from shaking and stalling when starts.Any problem, please contact our store without hesitation. Honor to serve you.Specifications:Name: Planetary Gear Reduction UnitColor: BlackMain material: SteelItem Weight: 98.8gSuitable for: 1/10 RC CarPackage Information:Package Weight: 100gPackage Size: 9 * 5 * 4.5cm / 3.54 * 1.96 * 1.77inPolybag packageNote:The included steel pinion goes onto your motor, then use your original pinion on the output shaft of this gear reduction unit.This product is designed for regular 540 brushed motor, its not designed to run on high power brushless motors. It will work, but it wont last a long time.Package List:1 * Gear Reduction Unit