A Barrel is a type of watch component that holds and winds the mainspring, which is the power source that runs the watch. The barrel is made up of two parts: an outer drum and an inner arbor. The drum is typically made of steel and has a series of gear teeth cut into its circumference. The arbor is a cylindrical metal shaft that fits inside the drum and is connected to the mainspring. The drum is rotated by the winding stem, and as it turns, the gear teeth wind the mainspring around the arbor. The barrel ensures that the mainspring is wound evenly and helps keep the mainspring from becoming over-wound.
