[Hardened Steel 5mm Pinion] Made of highest quality hardened steel, the pinion gear provides durability and strength for a more enjoyable RC racing experience. With a reusable design that can withstand the wear and tear of continuous use, you can race with confidence, knowing that is built to last. [What You Get] You receive 4pcs (19T 20T 21T 22T) Pinion Gears, Grub Screws for each gear, a L hex key for easy installation, and a 5mm to 3.175mm shaft coupler allows your Mod 1 5mm pinion gear to match 1/10 RC car's motor. [Suitable For] 5mm/3.175mm Shaft Size Motors, For For 1/8 1/10 Scale RC Car Truck . [NOTE] Increase your speed safely and avoid overheating issues by starting with the smallest tooth size 5mm pinion gear and gradually moving up to larger sizes 5mm pinion gear. Throughout the run, make sure to monitor the temperatures of your ESC and motor, so you can adjust your speed and avoid any potential damage or malfunctions. [Compatibility] For proper compatibility between your 5mm pinion gear set shaft and RC motor shaft, it's important to make sure that both components have a diameter or bore of 5mm. M1 pitch determines the space between each tooth on the pinion gear 5mm,it's critical to match the pitch of your pinion gear to that of your spur gear to prevent any problems with teeth meshing.