Garage door extension springs have been for years the most common springs seen for opening a garage door. Torsion springs are used for this purpose as well, but are a more refined and sophisticated type of spring which is gaining in popularity. Most overhead Garage Doors feature extension springs, but you can always request torsion springs if you want. Double automated doors usually feature torsion springs.
The extension spring looks like the old fashion box spring you see in mattresses. They are located at the sides of the door and are mounted on the swing arms. They have a hook on each end and when purchased, they will be in their compressed state. Because they have no protection factors when stretched, it is the more dangerous of the two springs. It is also more inexpensive compared to the torsion spring.
Its main difference from torsion springs is that the operation of the extension spring is based on distance; the further it is extended, the more force is applied on the spring. It can last from 5,000 to 10,000 lifts.
Torsion or Torque springs are twisting steel which retains the force in the twist of the internal bar. If you think of the old fashioned mouse trap you have the idea. The power is created by twisting the mouse trap under pressure. The torsion spring's force is proportional to how the torque in the twist. This is usually an enclosed unit and thus safer than the loose spring. Torsion springs are located at the upper section of the door and are usually mounted on the door header. This kind of spring will be the far stronger of the two and can lift a weight up to 500 lbs. It has a lifespan of approximate 20,000 lifts.