These miniature bearing are made of high quality steel and ceramic for low noise and long service life. Bearing with ceramic balls is better resistant to corrosion and rarely require lubrication. These 608 bearing are specially designed for inline roller skate to improve speed. The lighter balls allow the bearing to faster, and uses less energy to maintain its speed. Inner Diameter: 8mm / 0.31inch Outer Diameter: 22mm / 0.86inch Thickness: 7mm / 0.27inch Colour: black + white Material: mixed materials Package Contents: 16 * Bearings Only the above package content, other products are not included. Note: Light and different displays may cause the color of the item in the picture a little different from the real thing. The measurement allowed error is +/- 1-3cm.