... -50mmChemical CompositionsteelCertificationISO9001Polish ball/ Grinding ball/grinding media1) Chrome steel grinding balls; AISI52100 Chrome steel, through hardness 62-65 rockwell '' C'' ,super-fine surface ,available ... 25.4mm3) Stainless steel grinding balls: AISI302, 304, 316,420,440 , Super-fine surface available 2mm to 25.4mm Polish Ball/grinding ball