6. Ball lot: a number of steel balls which assume that manufacturing conditions are same and can be regarded as a whole.
7. Mean diameter of ball lot: in the ball lot, the arithmetic mean of mean diameter between the largest steel ball and the smallest steel ball.
8. Variation of ball lot diameter: in the ball lot, the difference of mean diameter between the largest steel ball and the smallest steel ball.
9. Ball grade: the specific combination include size, shape, surface roughness and sorting tolerance of steel balls.
10. Ball gauge: the difference between mean diameter of ball lot and nominal ball diameter, which is a quantity in the set.
Note: Each ball gauge is integer multiple of ball gauge spacing determined by the ball grade.
11. Deviation of a ball lot from ball gauge: mean diameter of ball lot minus the sum of nominal ball diameter and the ball and ball gauge.
12. Ball subgauge: a quantity in the set that is closest to the actual deviation of a ball lot from ball gauge.
13. Deviation of a ball lot from ball dimension: the difference between mean diameter of ball lot and nominal ball diameter.
14. Hardness: A measure of the compressive capacity determined by a specific test method.
Note: For steel balls, the test method is generally Rockwell hardness method.