Thin-Section Ball Bearings Item: SMR137ZZ Structure: Deep Groove Material: 440C Stainless Steel ( prefix "S" ) Bore Dia (d): 7 mm Outer Dia (D): 13 mm Width (B): 4 mm Closures: Metal Shielded(ZZ) Lubrication: Grease Magnetic: little Hardness: 58HRC