Bearing Type: Hybrid Ceramic Bearing Beads: 7 Black Ceramic Beads for Inline Skate / Skateboard / Freeline Skate / Drift Board / Longboard Suit Rotation Element: 7 Black Ceramic Beads, High Temperature, Abrasion Resistant, High Rotation Black Ceramic has better hardness and compression strength than white ceramic Bearings Bearing Ring: High Quality Bearing Steel Cage: Nylon Suitable for high-corrosive environments and high-speed scenes Shielding: Double Sided Dust Cover Size: 8. x 22 x 7 (Inner Dimensions x External Height) / Unit: Limit Speed: 22,000 rev/min Tolerance Class Comparison: ABEC-9 Note: Bearings are hybrid black ceramic bearings. Do not use for strong impact actions such as jumping and do not need to use lubricant