Synthetic rubies (sometimes synthetic sapphires) used as bearings at the heaviest points of wear in a watch movement in order to reduce friction between moving parts and increase a movement’s lifespan. Jewels have a naturally slicker surface than metal — for example, the coefficient of friction between two pieces of steel is about 0.58, while the coefficient of sapphire on steel is about 0.15. Jewels are only used to increase the accuracy of the movement and are not for decoration.
« Back to Glossary Index