... CompositionsteelCertificationISO9001Polish ball/ Grinding ball/grinding media1) Chrome steel grinding balls; AISI52100 Chrome steel, through hardness 62-65 rockwell '' C'' ,super-fine surface ,available 2mm ... hardened, AISI1065 Through hardened, Super-fine surface available, 0.5mm to 25.4mm3) Stainless steel grinding balls: AISI302, 304, 316,420,440 ...