Mainplate
The mainplate is the base plate of a movement. Every other part, including the wheels, bridges, winding mechanism and pallet, is mounted onto it. Its holes and seats locate each part in exactly the right place. Its diameter usually defines the movement's diameter, since it is the foundation everything else sits on.
At a glance
- Job
- Base plate that every part is mounted onto
- Form
- Flat metal disc machined with holes and seats
- Significance
- Its diameter usually defines the movement diameter
If one part gives a movement its shape, it is the mainplate. A watchmaker begins assembly with it and builds everything else on top, so the accuracy of the plate sets the accuracy of the whole movement.
The foundation everything sits on
The mainplate is a flat metal disc machined with holes, seats and steps. These features locate the gear train, the winding mechanism and the pallet, each in its correct position.
- Location: the lower pivot of each wheel drops into a hole in the plate, which is where alignment comes from
- Bearings: the high-friction holes receive jewels pressed into the plate
- Foundation: the bridges above are screwed to the plate and hold the upper pivots of the wheels
Why its diameter defines the movement
Because the plate is the base for every part, its diameter is usually the rated diameter of the movement. When a maker designs a movement family, the plate size is settled first. For the wider movement family see the movement page, and for a real example read our guide to the best Japanese watches.
Examples
On an automatic watch with a display caseback you can see the mainplate beneath the bridges and wheels, and notice how every part sits on top of it.
View this watch
Comparison
The mainplate and a bridge together form the frame of a movement, but they play different roles.
| Option A | Option B | Notes |
|---|---|---|
| Mainplate | Bridge | The mainplate is the single base that holds the lower pivots of the wheels; a bridge is a smaller upper piece screwed onto the plate that secures the upper pivots. |
Related terms
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Frequently asked questions
What does the mainplate do in a watch?
The mainplate is the base plate of a movement. Every other part, such as the wheels, bridges, winding mechanism and pallet, is mounted onto it. Its holes and seats locate each part in exactly the right place, so the movement is correctly aligned.
Why does the mainplate define the movement's diameter?
Because the plate is the base that every part sits on, and everything else fits within its outline. As a result its diameter is usually the rated diameter of the movement, and a maker settles the plate size first when designing a movement.
What is the difference between the mainplate and a bridge?
The mainplate is the single base that holds the lower pivots of the wheels. A bridge is a smaller piece screwed onto the plate that secures the upper pivots. Together they form the frame of the movement, but the plate is the foundation.