Dual Spring Replacement

Garage Door Torsion Springs are normally centered above the garage door on a one inch shaft. ... The shaft running through the springs transfers tension from the springs to the cable drums at the end of the shaft. These drums pull on the cables, which pull on the bottom of the door to balance the weight of the garage door.
 
With a dual spring system, there is a center bracket that connects the two springs together, which essentially turns the 2 springs into one. Usually only one of the springs will break, however, replacing both springs is HIGHLY recommended as the other spring will break very soon after. For normal sized garage door springs.
 
Price Veries depending on the size of the springs.