The watch stones are used in particular for the manufacture of bearings which support the pivots of axes of the wheel in steel . They are then presented (see drawings opposite) in the form of a drilled disc (to hold the pivot in its horizontal axis) or a flat disk applied against a drilled disc (counter-pivot, limiting the ebat in the axis vertical). They also serve as pallets at the anchor (parallelepiped shape), an ellipse fixed on the pendulum which receives the pulse (ellipse, triangle or half cylinder), or much more rarely a friction cylinder in certain cylinder watches (Tube segment).
The primary goal is to minimize the friction , which is extremely reduced from the metal on the stone.
On the other hand, given the very high relative pressures (when comparing the torque transmitted by the gears in relation to the extremely low surface pivots (15/100 mm in diameter for most purposes), the platinum of shows Being metal itself, metal-to-metal friction would inevitably induce short-term seizure of the bearing after the oils have lost their effectiveness (an inevitable condition for a watch operating for several consecutive years).
The various watch stones (“cushion”, “counter-pivot”, “palette”, “ellipse”) which are used to reduce friction are generally synthetic corundum and reddish-pink. Variants, rather rare, use blue stones, even diamonds. Formerly, bearings have also been made of other synthetic materials, with a red plastic appearance. The use of natural rubies originally was quickly supplanted as soon as the Verneuil method was used to create synthetic stones, much more homogeneous and less fragile than natural stones. In the larger format mechanisms, the bearings are formed directly in the material of the plates themselves or in the form of “plugs”