As thin as a sheet of printer paper at the tip, these Renishaw probe styli fit into grooves, lines, and threads that are too narrow for ball styli. The end is tapered, so to avoid measurement errors, you should only use these styli in shallow grooves that are wider than the end diameter. Otherwise, the end might inadvertently touch the sides of the groove before it touches the bottom. When they touch a workpiece, they trigger your coordinate measuring machine (CMM) probe to send a signal and measure geometric features.