**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.