What are Jewel Bearings in a watch?

A mechanical movement is composed of moving parts, such as gears, wheels and pinions. These parts are rotating on pivots (a vertical axis crossing the wheel). However, some has to consider that, for example, the fourth wheel of a watch makes a full circle on its axis once per minutes, meaning that it does 1440 full rotations a day or 525 600 full rotations a year. And this is not even the fastest wheel of a watch… Thus, you have to imagine the forces applied on the axis of such a wheel, even if it’s small and light. This is why it is harmful to insert the axis of such a wheel directly in the main-plate of the movement – considering the metal vs. metal frictions. Even with modern lubricants, it will slow the movement of the wheels down – ruining the accuracy of the watch – and at a certain time, wheels will simply block. Jewel bearings are the solution.

Jewels (rubies) are used as bearings to reduce friction at critical points, to improve the accuracy and durability of watches. One of the hardest materials after diamond, ruby (a corundum) do not wear – almost. As a consequence, jewels can be made very smooth which allow low friction with metal pivots. Last, they have a very good temperature stability and are acid-resistant.