CMM Ruby Ball Stylus Features include... 4mm Diameter Ruby Ball 100mm Length Ceramic Stem M4 Threads This straight stylus is designed to inspect simple features where direct, unobstructed contact with a measured surface is possible. The Ceramic Stem offers stiffness comparable to steel, but is significantly lighter than tungsten carbide. This ceramic stemmed styli can also offer additional crash protection to your CMM Probe as the stem will shatter in a collision, protecting your probe.