with high quality Spindle Interface Type: Hollowgram SI/SL/Compact Compatible with: Time Trial, Triathlon, Cruiser, Cyclocross, Dirt Jumper, Folding, Mountain, Recumbent, Road - Racing, Road - Touring, Track, Tricycle, Unicycle, Urban Fixed Gear bicycles Oil-free self-lubricating ceramic ball bearings do not require grease Provides electrical insulation between inner and outer rings due to ceramic rolling elements Higher rotational speed capability compared to standard bearings Suitable for wet and high-temperature environments; resistant to water washout and degradation Waterproof design allows reliable operation in wet conditions Surface roughness: Ra 0.05 Model Number: Ceramic Ball Bearing Color: Silver + Black Material: Rubber + Ceramic Dimensions: Inner Diameter: 30mm Outer Diameter: 42mm Thickness: 7mm Package Contents: 2 x 6806 Ceramic Bearings Note: Product colors may vary slightly due to lighting and monitor display differences. Measurement tolerance: +/- 1-3 cm