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## How to judge the quality of a ball?

The quality of a ball is defined by size, surface hardness, surface integrity and deviation from spherical form. See below instructions:

Size is the mean ball diameter, arithmetical mean of the largest and the smallest of the single diameters of a ball.

Surface hardness is usually measured on Rockwell scale.

Surface integrity is measured as surface smoothness and no defects like flats, pits, soft spots and cuts. Balls must have no such defects on visual inspection.

Deviation of spherical form defines whether the ball is out of ball shape.

## Other definitions of steel ball:

Nominal ball diameter: diameter value which is used for the general identification of a ball size.

Single ball diameter: distance between two parallel planes tangential to the actual surface of a ball.

Mean ball diameter: arithmetical mean of the largest and the smallest of the single diameters of a ball.

Variation of ball diameter: difference between the largest and the smallest of the single diameters of a ball.

Deviation from spherical ball surface: various types of deviation from the perfect spherical ball surface, uniformly or non-uniformly distributed and repeated around the ball surface.

Deviation from spherical form: radial distance between the smallest circumscribed sphere and the greatest inscribed sphere, with their centres common to the least squares sphere centre.

Waviness: surface irregularities of random or periodical deviation from the ideal spherical form.

Surface roughness: surface irregularities with relatively small spacings, which usually include irregularities resulting from the method of manufacture being used and/or other influences.

Surface defect: element, irregularity or group of elements and irregularities of the real surface, unintentionally or accidentally caused during manufacture, storage, handling or use of the surface.

Ball lot: definite quantity of balls manufactured under conditions presumed uniform and which is considered as an entity.

Mean diameter of ball lot: arithmetical mean of the mean diameters of the largest ball and the smallest ball in a ball lot.

Variation of ball lot diameter: difference between the mean diameters of the largest ball and the smallest ball in a ball lot.

Ball grade: specific combination of dimensional, form, surface roughness and sorting tolerances for balls.

Ball gauge: amount by which the mean diameter of ball lot should differ from the nominal ball diameter, this amount being one of an established series.

Deviation of a ball lot from ball gauge: difference between the mean diameter of a ball lot and the sum of the nominal ball diameter and the ball gauge.

Ball subgauge: amount, of an established series of amounts, which is the nearest to the actual deviation from the ball gauge of a ball lot.

Hardness: (rolling bearings) measure of resistance to penetration as determined by a specific test method.