The balance cock is a cantilevered bridge, typically secured to the watch's mainplate by a single screw. It serves as the upper support for the balance staff—the axle upon which the balance wheel oscillates—enabling the watch to keep time.
Amateur watchmakers often encounter specific issues when assembling or repairing this component: amateur cock
: The most delicate step is ensuring the upper pivot of the balance staff perfectly enters the jewel hole in the cock. If the screw is tightened while the pivot is misaligned, the staff will break. The balance cock is a cantilevered bridge, typically