Ceramic Skate Bearings Diamond Polished Super Light Silicon Nitride Ceramic Balls. ABEC 7. 8mm inner diameter x 22mm outer diameter x 7mm width 608 size Highly polished races with high performance low friction nylon inner cage + proprietary inner tolerances Oiled with ACER Racing's SIN 100% synthetic lightweight oil Sealed on both sides with no contact removable seals AUTHENTICITY GUARANTEED ONLY WHEN PURCHASED FROM ACER RACING: OTHER SELLERS ARE COUNTERFEIT