... are robust in operation, requiring little maintenance.Ball Bearing Features: Shield / closure: Open ball bearing, Z, ZZ, RS, 2RS, 2RZ ... , C4, C5 Ball bearings material: AISI52100, AISI440C, AISI304, AISI316, ceramic Retainer: PTFE, nylon, or stainless steel Hardness for rings and ... , Deep groove ball bearings are the most widely used bearing type. Consequently, they are available in many executions and ...