Their crystal structure and zero porosity permit microfinishes of 2 to be attained. Other features of the materials include extreme hardness, chemical inertness (even to hydrofluoric acid), low-friction coefficient, high thermal conductivity, and excellent wear resistance.

Ruby balls are used in chemical pump-check valves, wind indicators, probe and test-measurement tips, medical check valves, ball-point pens, master ball gauging sets, ball plug gages, sapphire fiber-optic lens systems, tracer tips, gyroscopic wear points, and precision metering-valve assemblies. Sapphire balls can be drilled for use as precision jeweled bearing rollers for low-friction and long-wear applications. The balls' 2,000°C melting point makes them suitable for high-heat applications with no oxidation.

Bird Precision,
One Spruce St., Box 540569,
Waltham, MA 02454,
(800) 454-7369,