... AISI52100 Chrome steel, through hardness 62-65 rockwell '' C'' ,super-fine surface ,available 2mm to 25.4mm2) Carbon steel grinding balls ... Case hardened , AISI 1085 through hardened, AISI1065 Through hardened, Super-fine surface available, 0.5mm to 25.4mm3) Stainless steel grinding ... balls: AISI302, 304, 316,420,440 , Super-fine surface available 2mm to 25.4mm Polish Ball/grinding ball