shorten torsion spring life. Owners are advised to avoid applying grease to garage door tracks because that makes the wheels "skate" in the track instead of turning on their bearings. Only bearings, hinges, and spring wire require lubricant. Extension spring lift mechanism An extension spring counterbalance system consists of a pair of stretched springs running parallel to the horizontal tracks. The springs lift the door through a system of pulleys and counterbalance cables running from the bottom corner brackets through the pulleys. When the door is raised, the springs contract, thus lifting the door as the tension is released. Typically these springs are made of 11 gauge (3 mm) galvanized steel, and the lengths of these springs are based on the height of the garage door in question. Their lifting weight capacity can best be identified by the color that is painted on the ends of the springs. Maintenance Maintenance of garage door is described in the manufacturer's instructions and consists of periodic checks for correct operation, visual inspection of parts, and lubrication. Safety Garage doors can cause injury and property damage (including expensive damage to the door itself) in several different ways. The most common causes of injury from garage door systems include falling doors, pinch points, improperly adjusted opener force settings and safety eyes, attempts at do-it-yourself repair without the proper knowledge or tools, and uncontrolled release of spring tension (on torsion spring systems). A garage door with a broken spring, or the wrong strength spring, can fall. Because the effective mass of the door increases as the garage door sections transfer from the horizontal to vertical door tracks, a falling garage door accelerates rapidly. A free-falling garage door can cause serious injury or death. The sections and rollers on garage doors represent a major pinch hazard. Children should never be allowed near a moving garage door for this reason. On manually operated garage doors, handles should be installed vertically, to promote "vertical orientation of the hand". Mechanical garage door openers can pull or push a garage door with enough force to injure or kill people and pets if they become trapped. All modern openers are equipped with “force settings” that make the door reverse if it encounters too much resistance while closing or opening. Any garage door opener sold in the United States after 1992 requires safety eyes—sensors that prevent the door from closing if obstructed. Force