All CeramicSpeed Bearings are hand-built in Denmark. Super-smooth CeramicSpeed grade 3 Silicone 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 optimized with a low-viscosity CeramicSpeed All Round Grease to minimize friction 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. During the building process, we check each bearing four times by hand to ensure that all parts are matched perfectly. CeramicSpeed Balls are 400% smoother, 128% harder, and 58% lighter than standard steel bearings normally used in the bicycle industry. When comparing the CeramicSpeed Balls with other ceramic balls in the industry, you will find that the CeramicSpeed Balls are 15% harder, take 99% higher loads, and are 100% smoother. - Inner Diameter: 17mm - Outer Diameter: 26mm - Width: 5mm