A bridge is a metal plate in a watch movement that holds the pivot of at least one moving part. It rests on two supports and is fixed to the main plate. Together, the bridges and the main plate make up the frame of the movement.
How is a bridge fixed in place?
A bridge carries the pivots of one or more wheels. It is held at both ends, and each end has a foot and a screw. In modern movements, separate plates or bars called bridges take the place of a single back plate. Because each bridge is separate, it can be taken off and refitted together with the wheels it holds.
Not to be confused with
A cock differs from a bridge in how it is held. A bridge is fixed at both ends, but a cock is fixed at only one. That makes it a cantilever, a part supported on one side only. To stay rigid, a cock must be kept short. The balance wheel is mounted on a cock, not on a bridge.
Where it comes from
Jean-Antoine Lépine’s calibre swapped the pillars and the upper plate for bars and bridges. Instead of one upper plate, the movement had separate parts. Lépine came up with a thinner pocket-watch design in about 1764 or 1765. The earliest Swiss pocket-watch bridge movements date from about 1900. They used three bar-shaped bridges laid side by side.
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