The ZERØ ceramic bearings have ceramic balls and steel races. The balls are Grade 3, Silicon Nitride. These are the roundest balls you can buy without a military license. The races are treated with a black oxide coating, which helps prevent rusting in the bearing. The races are then re-ground to a mirror finish after this treatment. Finally, they are cryogenically treated for strength before assembly. We also use Silicone VV seals, which is the lightest drag seal available on the market.