Ball quality is defined as follows:

Surface Hardness is measured on the Rockwell Scale. Minimum hardness is RC 60 for carbon, chrome and 440 stainless balls and varies for other products according to the material and desired toughness.
Case Depth is the radial distance from the ball surface to the point where hardness falls to Rockwell C 50. The core is the remaining soft inner area (avalible in carbon steel ball).
Surface Integrity is defined as the surface smoothness and freedom from defects such as flats, pits, soft spots and cuts. Balls must be free of such defects when inspected without magnification.
Size is the mean diameter, measured between two parallel planes on the ball surface.
Sphericity is defined as the deviation from a true spherical form (out-of-round condition).

Standard