Select from 2004 and newer Mavic Ksyrium SL - ES or 2005 and newer Zipp. Enduro manufactures the finest quality bearings & seals for original equipment or replacement applications for superior performance. Made from pure Silicon Nitride material with extreme high density from uniform compaction (3.25 g/cm3), the micro-structural development of this material during manufacture is second to none. These high precision Grade 5, SI3N4 pure ceramic balls are 5/1,000,000" from exactly round in sphericity. 60% lighter weight, and 7 times harder than steel, friction is reduced to near zero. Resistance to heat is 8 times greater than that of steel while there is simply no comparison for corrosion resistance.