HPI 46 tooth Nitro spur gear is constructed of black nylon, adapter type spur gear. This will only work on Two-speed transmissions that have the HPI 1st gear adapter type construction. The included gear ratio chart list recommends gears for specific HPI vehicles. INCLUDES: One 46 Tooth Nitro Spur Gear One Gear ratio chart and installation guide Required Parts HPI Nitro Two-speed transmission or heavy duty first gear adapter