1.low noise,low libration 2.seals type:open,seal,shield 3.high-end technology The same size can be made of different materials, including,Stainless Steel BearingsChrome Steel BearingsCarbon Steel BearingsCeramic BearingsMax Load (kgf)Dyn:155Stat:70RPM (x1000):41Shield / closure: Open Bearing, Z, ZZ, RS, 2RS,TTTolerance codes: ABEC-1, ABEC-3, ABEC-5, ABEC-7Vibration level codes: V4, V3, V2, ...