Synthetic rubies used in a watch movement. Some jewels are used as bearings to reduce friction. They’re set in holes drilled into the movement plate and bridges, and hold the rotating pivots of the movement’s gears and wheels. Jewels are also placed on top of the balance-pivot jewels (these are called “endstones”) where they rest against the tips of the balance staff pivots. Because of their hardness (ruby, a type of corundum, measures “9″ on the Mohs hardness scale where diamond measures 10), jewels are also used in the escapement to engage the teeth of the escape wheel (these are called “pallet jewels”) and on the roller (this is called the “roller jewel”).