Garage door torsion spring, wound on the pole above the top of the garage door opening
Garage door extension springs are mounted on either side of the door and extend along the horizontal portion of the track when the door is closed
You may also have an old one-piece door that swings outward as it goes up and up. This special design mounts the springs on either side of the doorway - about the height of your waist, attached to a lever bracket system that extends the spring toward the ceiling when the door is closed. This is an old and extremely dangerous system that is no longer manufactured. If you have such a system in the garage, I highly recommend replacing it.
Garage door torsion spring - Single or double spring design. The spring typically breaks under maximum stress, either when the overhead garage door is closed/down, or if it has been completely closed (usually). If you close it manually and it happens during this operation, don't try to stop it from crushing and let it go... well, unless your feet are the place where the goalkeeper slams!
When one of the two garage door springs breaks, you need to replace them at the same time! It will cost some extra money, but installing new and old springs will:
More nervous about new
The goalkeeper loses the proper balance
The remaining old garage door springs are likely to burst soon
Torsion springs for residential overhead garage doors have a life of 5000-30000 cycles. These numbers represent the average total number of times the door should be able to open and close before the garage door spring is expected to be replaced.