This front sprocket is used on the Chinese 33cc, 36cc, 43cc, 49cc & 52cc engines, specifically pocket bikes, mini choppers, even gas skateboards. May be used on other applications as well. This sprocket has 25 teeth and is compatible with #25 chain only. Sprocket details: 25 Tooth 6 Spline ID Across Teeth: 11.1mm (.43″) ID Across Valley: 14mm (.55″) OD: 53mm (2.09″) Height: 11.8mm (.47″) Be sure to measure your chain or current sprocket before ordering. Most Chinese sprockets have the chain size and tooth count stamped into the metal.