1. Hybrid Ceramic bearings,do not need Grease,it have special rustling sound,Super High Speed,Long Spin time. | 2.Rolling elements:7 Black Ceramic Beads(Si3N4), High Temperature and Corrosion Resistance,Abrasion resistance,High Revs. | 3.Size: 8 * 22 * 7 (Inner * Outer * Height) / Unit: mm | 4.The Bearings have High Speed and High temperature resistance,But It Do not Suit For Extreme Sport , Like