This Belt Drive Sprocket sits on the shaft on top of the power (motor) head. The belt goes around the sprocket and the teeth on it grip the belt so it stays on track. This is used on multiple Genie model garage door openers that have the belt drive rail system. Compatible with Genie Models; 1028, 2028, 3020H, 3020HB, 3024, 3042, 4024, 4042, SilentMax 1000, SilentMax 1200, ReliaG 650, ReliaG 850 Includes replacement instructions If you do not see your model on this list and have questions please contact us for compatibility questions Genuine Genie Replacement Part