The screw drive carriage assembly has teeth inside it that connect to the screw inside the rail. This allows smooth operation of running the door up and down the rail. If the motor on your operator is running, the screw drive is turning, but the door is not operating it may be time to replace the carriage. The carriage is designed to protect the screw drive from wear and tear Genuine Genie replacement part Compatible with Models: 2564, 2568, 3064, 4064, 2562, 3062, 4062, 4063