Product Description: Compatibility: This front sprocket is intended for use with Chinese 200cc engines, specifically designed for the Coleman CT200U mini bike, and may also be suitable for other applications. It is compatible with the 420 chain ONLY. Sprocket Details: Chain Pitch: #420 Teeth Count: 10T Inner Diameter: 16mm (0.66 inches) Requires a 5x5x28 key (Not included) Measurement Reminder: To ensure compatibility, please measure your chain or existing sprocket before making a purchase. The 420 chain has a 1/2" pitch and a 5/16" roller diameter. Most Chinese sprockets display the chain size and teeth count stamped into the metal.