【High quality hardened metal&Work Smoothly】0.8M pinion gear set is of hardened metal construction. Last longer life. Good machining made less rough and less noise than other pinions that make them roll smoothly. 【Pitch & Teeth】Compatible with 0.8 metric (0.8M) pitch. 20T 21T 22T 23T 24T is the number of teeth on the pinion gear. Please make sure your spur gear and pinion gear have the same pitch, or the teeth won't mesh. 【Compatible with】Compatible with 1/8 inch Hole, 3.175mm Shaft Size Motors, Make sure your RC motor shaft have the same diameter 【Free combination】The speed depends on your gear ration. We provide five different teeth pinion gear to make you more choice in gear ration. 【Package Include】The package included 20T 21T 22T 23T 24T pinion gear and a hardened hex key. 0.8M Hardened Steel Pinion Gear Set 1/8 inch 3.175mm Hole 20T 21T 22T 23T 24T with Hex Key for RC Brushless Brush Motor RC Car Upgrade(Compatible with 0.8 Metric Pitch)