An upgrade option for cartridge wheel bearings that offer extremely low friction, improved power transfer, and a service life that far exceeds traditional steel bearings. Features: Grade 3 Silicon Nitride balls Hardened races Reinforced polyamide cage and non-contact seals Hand built in Denmark High resistance to poor lubrication Specs: Thickness7mm Bearing I.D. (mm)17mm MaterialCeramic Bearing O.D. (mm)30mm