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Tamiya 89916 4-Speed Crank-Axle Gearbox Kit - Clear

Vendor's Description: 

This gearbox has four possible gear ratios, including the highest gear ratio of Tamiya’s gearbox series, 5402:1. The other options are 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.