This unit has two cables which each wind around a pulley on the far left and right of the unit, just under the door. One end of the cable connects to the door, and the other end connects to the springs, one on each side. The cables wrap around the pulleys. When the door opens, the springs stretch and counterweight the door. I took off the lower panel, hooked the cables to the old springs, installed the cables, and reinstalled the lower panel. Total time about 10 minutes.