ZIPP CeramicSpeed Bearing Kit – 61903 Modified – ZIPP 177 Rear Hub Shell (includes bearings and one grease syringe):

Zipp:

For cyclists looking for that extra advantage. Ceramic Speed bearings. Use with ZIPP hubs and free hub driver bodies. Lowest resistance hybrid ceramic, ceramic balls and steel cages available. Measurable wattage savings between 1.5 and 9 watts per bearing set.