with high quality Spindle Interface Type: , Hollowgram SI/SL/Compact For Bike Type: Time Trial Triathalon, Cruiser, Cyclocross Bike, Dirt Jumper, Folding Bike, Mountain Bike, Recumbent Bike, Road Bike - Racing, Road Bike - Touring, Bike, Track Bike, Tricycle, Unicycle, Urban Bike - Fixed Gear. Oil-free self-lubricating, ceramic ball with oil-free self-lubricating properties, so ceramic ball bearings cannot grease Insulation, rolling body with ceramic ball, you can achieve the bearing between the inner and outer ring insulation High speed, the use of ceramic ball speed than the general bearing speed is much higher , ordinary bearings in the water and high temperature environment, the oil is easy to wash or kill, so that the bearings soon bad, the use of ceramic balls as a rolling body, do not worry about these problems. Waterproof: ordinary bearings used in the water, grease washed off, the bearings soon broken, the use of ceramic balls, you can normally use in the water. Roughness: Ra 0.05 Model Number: Ceramic Ball Bearing colour:Silver + black Material:Rubber + ceramic Diameter: Inner: .30mm Outer: .42mm Thickness: .7mm Package Contents: 4 x 6806 Ceramics Bearing Only the above package content, other products are not included. Note: Light reflection 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.