Pololu

With possible gear ratios of 39.6:1, 47.6:1, 61.7:1, and 74:1, the Tamiya 72007 4-Speed ​​High-Power Gearbox is well-suited for most applications ...

The primary feature of this gearbox is a worm gear, which locks the output shaft when the motor is not turning. Its high gear ratios of 84:1, 216:1...