Miniature bearings are made of high quality steel and ceramic for low noise and long life. Ceramic ball bearings are more resistant to corrosion and rarely require lubrication. 608 bearings are specially designed for roller skating to improve speed. Lighter balls allow the bearing to spin faster and use less energy to maintain its speed. Inner Diameter: 8mm/0.31inch Outer Diameter: 22mm/0.86inch Thickness: 7mm/0.27inch Color: Black + White Material: Mixed materials Package Contents: 80 * Bearings Only the above package content, other products are not included. Note: Light reflection and different displays may cause the color of the item in a little different from the real thing. The measurement allowed error is +/- 1-3 cm.