Garage door hardware use springs to lift the weight of the door. The springs are either side stretch springs or twist springs mounted on a torsion bar. Torsion bars are long tubes that attach the springs and cable drums. As you lift the door, spring twists twisting the torsion bar. The rope drums turn with the torsion bar in the cover for the cable. There are three basic types of torsion bar garage door configurations that are widely used in residential areas.
Standard Front torsion bar
Most standard size garage doors that use torsion bars have a standard front mount bar over the top of the door. The torsion bar is mounted on two brackets above the garage door slot and the head above the door. These types of torsion spring doors require the use of solid steel rods to wind the springs.
Low Rear Mount Torsion Bar
Garage gates require a certain amount of space between the top of the opening and the ceiling to work. Garage door hardware the space is smaller than an ordinary door track requires, it is necessary having a double low ceiling height track. Often the torsion bar on a low-headroom door is mounted on the rear of the upper grooves. These types of torsion bars work in the same way as the front mounting torsion bars but with subtle differences. The rope drums that the door cables wind on are mounted on the outside of the groove on the torsion bar. The spring on a bar low ceiling height torsion wind also opposite direction than a normal front torsion bar spring.