material of rings and retainer:PEEK,POM,PI,HDPE.PVDF.ABS.PP material of balls:ZrO2,Si3N4, stainless and glass long life Feature:1.material of rings and retainer:PEEK,POM,PI,HDPE.PVDF.ABS.PP2.material of balls:ZrO2,Si3N4, stainless and glass3. long life and easy usingAdditional serves:1. prompt delivery2. excellent quality and reasonable price Plastic bearing