... treatment with ball raceway More smoothly while lower noise 6021 ZZ/6021 2RS/6021 DDU/6021 VVDimension:d:105mmD:160mmT:26mmWeight ... to manufacture it.7. Shield/closure: Open ball bearing, Z, ZZ, RS, 2RS, 2RZ 8. Internal clearance: C2, C3, C4 ,C5 ... be more accurate. operating more smoothly while lower noise. 6021 ZZ/6021 2RS