Mainspring
The coiled spring that stores energy to power the movement.
What is a Mainspring?
The mainspring is the heart of a mechanical watch's power system. It is a long, thin strip of metal — typically around 20–30 cm when uncoiled — that is tightly wound inside a cylindrical container called the barrel.
When you wind a watch (either manually by turning the crown, or automatically through the motion of a rotor), you are coiling the mainspring tighter and tighter. This stores potential energy in the spring. As the mainspring slowly uncoils, it releases that energy through a series of gears and levers that ultimately drive the hands of the watch.
Why Mainsprings Need Servicing
Over time, mainsprings can:
- Fatigue and set — the spring loses its elasticity and cannot store or release energy as efficiently
- Break — a brittle or heavily worn mainspring can snap, stopping the watch entirely
- Corrode — moisture inside the case can cause surface rust
During a full service, the mainspring is typically replaced as a matter of course, even if it appears intact. A fresh mainspring ensures consistent power delivery and accurate timekeeping.
How Long Does a Mainspring Last?
Modern mainsprings made from alloys like Nivaflex can last 20–40 years under normal use. Vintage watches may have mainsprings that have been in place for 50 or more years — these almost always benefit from replacement.