Ball styli are the most general purpose. Completely round and smooth, the ball end won’t make contact with a workpiece at more than one point, preventing inaccurate readings. The ball is made of zirconia ceramic, which is tough enough to avoid fracturing from high-speed scanning jobs and frequent contact with rough or hard surfaces. Safe for use on cast iron, zirconia ceramic minimizes the friction that would otherwise damage both your workpiece and your styli. As a rule of thumb, you should choose a ball stylus with the largest ball-end diameter that works for your application. Larger ball ends reduce the possibility that the stem will accidentally touch your workpiece and interfere with the stylus’ reading.