Precious stone bearings are used in instrumentation. Bearings bearing instrument load is small, but to rotate high precision, good sensitivity, long service life. Gems with a small number of friction, high hardness, corrosion resistance, thermal expansion coefficient, high compressive strength performance, to meet the use of instrumentation bearings requirements. The production of gem shaft materials are corundum, agate, glass and so on. Corundum is a body of alumina, natural and man-made.