28mm or 32mm 

M2 Metal Treatment Services in PA USA has a unique coating process to the already high-quality Superior Bearing, which eliminates any microscopic imperfections in the bearings surface. Reducing friction, drag and enhancing oiling capabilities in which all adds to prolong the life of the bearing itself. 

Note* Pairing the treated M2 bearing with Dayton Day lube Nano Ceramic grease ensures a reduction in friction and rolling resistance which is exactly what you need to gain that edge against your competition. 

Sold Individually