CeramicSpeed Bearing. Features: All CeramicSpeed Bearings are hand-built in Denmark. Super smooth CeramicSpeed grade 3 Silicon Nitride balls are matched (within microns) with hardened steel raceways that feature an ultra-smooth polished groove. The balls are held in place by a reinforced polyamide cage. Every bearing is optimised with a low viscosity CeramicSpeed "Blue Grease" to minimise fiction and increase bearing life. Non-contact seals complete the bearings, keeping dirt and moisture out. CeramicSpeed Bearings can be used for any cycling discipline: Road, TT, Tri, Track, Cross and MTB. The benefits are super low friction, better power transfer and increased bearing life. CeramicSpeed Balls are 400% smoother, 128% harder and 58% lighter than standard steel bearings normally used in the bicycle industry. Specs: Bearing:61903 (6903) ID X OD X W Mm:17x30x7