The belt drive bullet assembly is the white piece that holds the belt for the garage door opener together. The carriage assembly for these models also attaches to this bullet assembly allowing it to move the garage door open and closed. 

• Assembly contains: 2 Bullet side pieces, and screws to install it
• Genuine Genie replacement part 
• Compatible with the following Genie models that have the belt rail: 1028, 2028, 3020H, 3020H-B, 3024, 4024, 3022, 3042, 3120H, 3120H-B, 4022, 4042, 4124, 4164 (ReliaG, IntellG, SilentMax, and TriloG, series with these model numbers)