Extension springs for garage doors work differently because they are mounted above the door's horizontal tracks, on the sides of the door. In most instances, residential garage doors are equipped with two extension springs. Commercial doors that are larger may require more extension springs for smooth operation. Extension springs can have either open loops, closed loops, or clip ends which secure the spring to the garage track hang, pulley, frame or pivot pin. Heavier garage doors may require additional extension springs in order to hold the weight and avoid premature breakage.