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, Tandem Bike, Track Bike, Tricycle, Unicycle, Urban Bike - Fixed . 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 Long life, 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. Surface Roughness:Ra 005 Model Number:Ceramic Ball Bearing colour:Silver + black Material:Rubber + ceramic Diameter: Inner: Approx30mm Outer: Approx42mm Thickness: Approx7mm Package Contents: 2 * 6806 Ceramics Bearing 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.