The mainspring is the coiled spring that stores energy inside a mechanical watch. When you wind the watch, you tighten that spring. As it slowly unwinds, it powers the gear train and keeps the movement running.
Where the mainspring lives
The mainspring is housed inside a barrel. The barrel helps contain the spring and transfer its energy into the movement at a controlled rate.
It does not directly move the hands on its own. Its stored force travels through the gear train, while the escapement and balance control how quickly that energy is released.
How it gets wound
- Manual-wind watch: turning the crown winds the mainspring.
- Automatic watch: a moving rotor powers a winding system that tightens the mainspring as the watch moves on your wrist. Many automatics also allow hand-winding.
What power reserve means
Power reserve is the amount of time a watch can run after its mainspring has been wound. The exact reserve depends on the movement. A watch may stop sooner than expected if it was only partly wound, if wrist movement was limited, or if the movement needs attention.
Can you overwind it?
Traditional manual-wind movements usually reach a firm stopping point when fully wound, so stop when you feel real resistance. Many automatic movements use a slipping bridle that helps manage continued winding, but that does not make rough crown handling a good idea. Wind slowly and follow the manual for the exact movement.
The mainspring is the energy source, not the timekeeper. The balance and escapement regulate how that energy becomes measured time.
Continue with our complete automatic watch owner's guide.