Renishaw offers a range of ball materials suited to scanning of different component materials. See the Styli and accessories - technical specifications guide (Renishaw part number H-1000-3200).
Stylus balls should be regularly inspected for damage or 'pick-up' of component material. Stylus balls, threads and mating faces should be cleaned using IPA and a lint-free cloth. Extra care should be taken with small stylus tips.