... steel Gcr15,PTFE, nylon, PEEK or (stainless) steel 2.Styles:OPEN,Z,ZZ,RS,2RS,2RZ.. door bearingbearings for windows and doors:1.Material:chrome ... , C56.Hardness:59 - 63HRC7.Retainer:PTFE, nylon, PEEK or (stainless) steel8.Application: doors, windows, wheel chair, skating shoes, textile machine and so on. bearings for windows and doors