In a mechanical watch movement, the barrel arborBarrel Arbor In a mechanical watch movement, the barrel arbor is a shaft that runs through the center of the mainspring barrel. The mainspring is wound around the barrel arbor, and as the mainspring unwinds, it powers the watch's movement by transmitting torque through the gears of the movement. [Learn More] is a shaft that runs through the center of 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] 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] . The mainspring is wound around the barrel arbor, and as the mainspring unwinds, it powers the watch’s movement by transmitting torque through the gears of the movement.