This Belt Drive Sprocket sits on the shaft on top of the power head. The belt goes around the sprocket and the teeth on it grip the chain so it stays on track. This is used on multiple Genie model garage door openers that have the belt drive rail system. (See below)

• Compatible with Models; 1055, 1155, 2055, 3053, 3055, 3155, 7055, 7155 SilentMax Connect, StealthDrive 750, SilentMax 750, SilentMax 550, QuietLift 550, StealthLift 500
• Genuine Genie Replacement Part