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Torsion springs are normally mounted horizontally above the opening of your garage door. When you pull the door down, cables attached to the bottom corners actually force the springs to wind up, in turn energizing the system.
There are two types of spring systems: a torsion spring system in which a single coiled spring running parallel to the door serves to counter to weight of the door; and an extension spring system in which two springs, one on either side of the door running parallel to the overhead door traces, does the work.