The barrelBarrel The barrel is a cylindrical container that holds the mainspring. The barrel is connected to the winding mechanism. The winding mechanism rotates the barrel, which in turn winds the mainspring. [Learn More] is a cylindrical container that holds the mainspringMainspring The mainspring is a spiral-shaped metal spring that stores energy in a mechanical watch movement. It is located inside the barrel. The mainspring is wound, either manually or automatically. The mainspring unwinds over time, and the watch will stop running when the mainspring is fully unwound. [Learn More]. The barrel is connected to the winding mechanism. The winding mechanism rotates the barrel, which in turn winds the mainspring.