All of our Extension Springs are sold in pairs. Select the overall weight of the door as each spring in the pair lifts half the doors weight. For use on Garage Doors that have Extension Springs rather than Torsion Springs. These springs run parallel to your garage door's tracks rather than mounted above the door. Our Extension springs come guaranteed for 10,000 cycles and are DASMA (Door & Access Systems Manufacturer’s Association) Color-Coded for easy referance. All of our Torsion and Extension Springs come Oil-Tempered to resist rust and corrosion. Extension spring are most commonly ordered by the weight and height of your garage door, and color coding is used to double check to see if your measurements are accurate.