Extension spring pair, 53 by 66 inches, for 12-foot-high garage doors. These cover door weights from about 80 to 280 pounds depending on the specific spring rating. Extension springs run along the horizontal track on both sides and stretch to counterbalance the door's weight as it opens. At 12 feet, you are dealing with a taller and heavier door than most residential setups, so the springs are bigger to match. Replace both springs together even if just one looks bad. Some sizes may need extra lead time, so check with us before ordering. Measure your door height and weight to get the correct pair.