A drive rack is a long steel bar with teeth along it that bolts or welds to the bottom of an automatic sliding gate. The gate motor sits on a pad at one end, with a small gear that grips the teeth. As the motor turns, the gear walks along the rack and pulls the gate with it.
Residential drive racks are usually 8 mm or 10 mm pitch (module 4), supplied in 1 m galvanised lengths. Bolt the lengths to the gate so the teeth line up perfectly across joins. Get the alignment wrong and the gear runs noisy and wears fast.
Mounting height is critical: the rack teeth must mesh with the motor pinion at the manufacturer's nominated centre distance, usually with 1 to 2 mm of clearance. CAD60 doesn't size the rack itself but locates it on the side elevation when an automated gate is selected.