Jewel Bearings are used in instruments to support the spindle which carries the pointer. The jewel bearing is made from a synthetic sapphire or ruby. It consists of a pivot hole in which the spindle rotates. 
Jewel bearings are also used in watches. They are chosen over metallic bearings as they have a very low coefficient of friction.
The bearings are made from synthetic sapphire or ruby which have no impurities or flaws. The advantages of jewel bearings are their long life, low friction and dimensional accuracy.