A cantilever rail is the backbone of a cantilever sliding gate. It is a strong, heavy beam that runs along the bottom of the gate and sticks out past the gate at one end as a tail. That tail balances the gate's weight. It is usually a heavy section like an 80x80x6 SHS, or a maker's own profile from a supplier such as Comunello or Combi-Arialdo, and the tail runs 30 to 50% of the opening width.
The rail rides over a pair of top rollers fixed to the receive post. Because the gate hangs off these top rollers, no ground track is needed. The driveway stays clear of any rail, channel, or trench.
CAD60 sliding-gate models compute rail length from the opening width plus the counterweight overhang, and place the roller positions on the side-elevation drawing.