Torsion spring
The tightly wound spring above a garage door that counterbalances its weight — and the one part you must never adjust yourself.
A torsion spring is the heavy steel spring (or pair of springs) mounted on a shaft above the garage-door opening. It stores energy when the door is down and releases it to do almost all the lifting, which is why the opener motor only needs to supply a small amount of force. That stored energy is also what makes it dangerous: a torsion spring under tension can release with enough force to break bones or worse if it's loosened, replaced, or it snaps. Lubricating the spring lightly is fine and is part of normal [garage-door maintenance](/guides/garage-door-maintenance), but winding, unwinding, or replacing it is strictly a job for a trained technician with winding bars. A door that won't stay put halfway open, or slams down, has a spring problem — call a pro. See [how to maintain a garage door opener](/guides/how-to-maintain-a-garage-door-opener).