Wheels Manufacturing Ceramic Sealed Cartridge Bearing 606 - 6 x 17 x 6mm

High quality ceramic bearings for higher performance
Ceramics are harder than steel, so they have less rolling resistence
Ceramics are more round than steel, also decreasing rolling resistence
Ceramics are much lighter than steel, decreasing overall weight
Ceramics require less lubricant, reducing maintenance
Heat treated steel races and sealed for longevity
Ceramics, due to their hardness, destroy foreign particles into a fine dust thus reducing wear to steel bearing races from said particles
These bearings are rated at grade 5 meaning they are out of roundness by 5/1000 of a millimeter, 500 % more round than the highest quality steel bearing, 6000 % more round than a low quality bearing
Typical weight reduction on a rear hub would be about 40 g though results may vary
Comes as a single cartridge bearing