The plate is the base plate supporting all the components of the mechanical movement of a watch . It is part of the draft . Normally made of brass , it can also be manufactured from precious metal , or synthetic sapphire .
The plate is provided
- Of the incrustations necessary for housing the other elements of the movement;
- Of screw threads necessary for fastening bridges ;
- A center hole allowing the passage of the pinions fixing the needles ;
- Two holes for fixing the dial on its upper part;
- Of a lateral thread on its upper periphery for fitting inside the watch case .
As a general rule, the plate and the bridges are decorated on their two flat parts. In the high-end, the sides and bottoms of the inlays are polished with diamond.
A protective layer ( gilding , chrome plating ) or a sub-micron layer of rhodium completes the treatment and ennobles the surface.
As a general rule, the plate covers the entire total diameter of the movement. Some movements are, however, equipped with a partial stage. This was already the case in the old movements of pocket watches developed by the American brands.