... robust in operation, requiring little maintenance.Ball Bearing Features: Shield / closure: Open ball bearing, Z, ZZ, RS, 2RS, 2RZ Ball bearings snap ring: N, NR ... clearance codes: C2, C0, C3, C4, C5 Ball bearings material: AISI52100, AISI440C, AISI304, AISI316, ceramic Retainer: PTFE, nylon, or stainless steel Hardness ...