Contact points of test indicators most often come with a standard spherical tip of 1, 2, or 3mm diameter. Many are of steel (alloy tool steel or HSS); higher-end models are of carbides (such as tungsten carbide) for greater wear resistance. Other materials are available for contact points depending on application, such as ruby (high wear resistance) or teflon or PVC (to avoid scratching the workpiece). These are more expensive and are not always available as OEM options, but they are extremely useful in applications that demand them.