The third wheelThird Wheel The third wheel is typically the first gear in the going train, and is connected to the mainspring barrel, which holds the mainspring. The third wheel receives power from the mainspring and transmits it to the center wheel. [Learn More] is typically the first gear in the going trainGoing Train The going train is a series of gears that transfer power from the mainspring to the escapement. It typically includes the third wheel, the center wheel and the escape wheel. [Learn More], and is connected to the mainspringMainspring The mainspring is a spiral-shaped metal spring that stores energy in a mechanical watch movement. It is located inside the barrel, a cylindrical container. The mainspring is wound by the wearer, either manually or automatically, through the movement of the wearer's wrist. The mainspring is the source of energy for the watch, and the tension in the mainspring determines the power reserve. 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] , which holds the mainspring. The third wheel receives power from the mainspring and transmits it to the center wheel.