Featuring 9 Moh hardness, Meller Sapphire and Ruby Balls come in 42 in. and metric sizes from 0.1–0.5 mm diameter with 0.000025 in. sphericity and ±0.0001 in. basic diameter tolerance. Units can be precision ground into plano-convex lenses with surface finishes to 80–20 scratch dig. Unaffected by fast moving dirt and impervious to most chemicals, solvents, and detergents, balls crafted into lenses for micro air vehicle applications are available A/R coated and provide 85–98% typical transmission.