The screw drive shuttle assembly sits inside the rail and attaches to the carriage assembly. When the shuttle is engaged to the carriage, the door will operate up and down the rail with the opener.   Emergency cord attaches to the shuttle assembly to allow the door to be operated manually when it is pulled and releases Comes with Shuttle only  Genuine Genie replacement part  Compatible with Models:  2562, 2564, 2568, 3062, 3064, 4062,4063, 4064