These are fast, real fast. Black ceramic, or Silicon Nitride is one of the hardest substances on earth. Black ceramic balls are much lighter than steel balls allowing them to spin faster, cause less vibration, and, because they do not rust or oxidize, require little lubrication. The inner and outer races are heat-hardened high carbon steel, titanium coated for protection against corrosion and rust. The deep grove in the outer race is especially designed to support high impacts and reduce rolling resistance.