Bridge
A bridge is a metal bar screwed over the mainplate that holds the upper pivots of the going-train wheels and balance in place. Fixed at both ends rather than one, it suspends each pivot between two anchor points. Bridges largely define the visible architecture and character of a mechanical movement.
At a glance
- Component type
- Metal bar carrying upper bearings
- Fixed at two ends
- Usually screwed to the mainplate at two points
- Common types
- Train, barrel and balance bridge
In a mechanical movement every wheel is held at both ends: its lower pivot sits in the mainplate, its upper pivot under a bridge. The bridge is the load-bearing part that keeps the pivot fixed and aligned so the wheel cannot wobble out of place as it turns. Without bridges the gear train would simply collapse.
What a bridge does
A bridge suspends the upper pivots of the balance and going train at a set height above the mainplate. The pivot holes usually carry jewels to cut friction and wear. A typical caliber has more than one bridge:
- Train bridge: carries the upper pivots of the going-train wheels, typically the center, third and fourth
- Barrel bridge: holds the upper bearing of the mainspring barrel
- Balance bridge: carries the upper pivot of the balance wheel
The shape, bevels and finishing of these bridges are a caliber's signature.
Visible architecture and skeleton watches
The pattern you see through a display caseback comes largely from how the bridges are laid out. In a skeleton watch the bridges are cut away to slim bars that hold only the pivots, leaving the mechanism on open view. Bridges are screwed to the mainplate, and together the two form the skeleton of the caliber. For the clean, sturdy bridge work of Japanese calibers, see our guide to the best Japanese watches.
Examples
Through a display caseback you can pick out the balance bridge easily: it is the metal bar that spans over the balance wheel and is screwed down at both ends. Even a plainly finished bridge is the first detail that reveals a caliber's layout and balance.
View this watchA practical way to recognize a bridge is to look for screws at both ends of the bar. A part fixed at only one end is not a bridge but a cantilevered cock, such as a balance cock.
Comparison
A bridge and a balance cock are often confused, yet the difference lies in how each is fixed.
| Option A | Option B | Notes |
|---|---|---|
| Bridge | Balance cock | A bridge is screwed at both ends and suspends a pivot between two points; a balance cock is a cantilevered part fixed at one end only, carrying the balance's upper pivot from its free end. Both do the same job, one is doubly supported, the other supported on one side. |
Related terms
Watches that show this
Frequently asked questions
What exactly does a watch bridge do?
A bridge holds the upper pivots of the wheels and balance at a fixed height above the mainplate. The lower pivot sits in the plate and the upper pivot under the bridge, so each wheel is held at both ends and stays aligned as it turns. Without bridges the gear train cannot stand.
What is the difference between a bridge and a balance cock?
The difference is how each is fixed. A bridge is screwed at both ends and suspends a pivot between two points. A balance cock is fixed at one end only and reaches out like a cantilever, carrying the balance's upper pivot from its free end. Both hold an upper bearing, one on two supports, the other on one.
Why are bridges so prominent in skeleton watches?
Because in a skeleton watch the mainplate and bridges are cut away to slim bars that hold only the pivots. The visible pattern of the mechanism comes largely from the shape and layout of the bridges, so bridge design directly sets the character of the watch.