# Steel Ball Terminology Description

1. Scope and field of application

This international standard specifies requirements for finished steel balls for rolling bearings.

2. Definitions, symbols, and explanations

2-1 Nominal ball diameter, DW：The diameter
value which is used for the purpose of general
identification of a ball size.

2-2 Single diameter of a ball, DWS：The distance
between two parallel planes tangent to the
surface of the ball.

2-3 Mean diameter of a ball, Dwm：The arithmetic mean of the largest and the smallest actual single diameters of the ball.

2-4 Ball diameter variation, Vdws：The difference between the largest and smallest actual single diameter of one ball.

2-5 Deviation form spherical form：The greatest
radial distance in any radial plane between a
sphere circumscribed around the ball surface
and any point on the ball surface.
Information regarding the measurement of the
deviation from spherical form is given in annex
B.

2-6 Lot：A definite quantity of balls manufactured
under conditions which are presumed uniform and which is considered as an entity.

2-7 Lot mean diameter, DwmL：The arithmetic mean of the mean diameter of the largest ball and that of the smallest ball in the lot.

2-8 Lot diameter variation, Vdwl：The difference between the mean diameter of the largest ball and that of the smallest ball in the lot.

2-9 Ball grade：A specific combination of dimensional, form, surface, roughness, and sorting tolerances.

2-10 Ball gauge S：The amount by which a lot mean diameter should differ from the nominal ball diameter, this amount being one of an established series.
Each ball gauge is a whole multiple of the ball gauge interval established for the ball grade in question. See also annex A.
A ball gauge, in combination with the ball grade and nominal diameter, should be considered as the most exact ball size specification to be used by a customer for ordering purposes.

2-11 Deviation from ball gauge, △S：The difference between the lot mean diameter and the sum of the nominal diameter and the ball gauge. See also annex A.

2-12 Ball subgauge：The amount of an established serried of amounts, which is nearest to the actual deviation form a ball gauge.
Each ball subgauge is a whole multiple of the ball subgauge interval established for the ball grade in question. See annex A.
The ball subgauge, in combination with the nominal ball diameter and the ball gauge, is used by ball manufacturers to denote the lot mean diameter and should not be used by customer for ordering purposes.

2-13 Surface roughness：All those irregularities of the surface which are conventionally defined within a section of the area where deviations of form and waviness are eliminated.

2-14 Hardness：The measurement of resistance to penetration as determined by specific methods.