ABMA Definitions

Grade: A specific combination of dimensional form and surface roughness tolerance. A ball grade is designated by a grade number.

Deviation from Spherical Form: Determined by rotation of the ball against a linear transducer with less than 4 grams gage force. The resulting polar chart is interpreted using the minimum circumscribed circle method (MCC) per ABMA std. 10.

Lot Diameter Variation: The difference between the mean diameter of the largest ball and that of the smallest ball in the lot.

Ball Diameter Variation: The difference between the largest and the smallest actual single diameter of one ball.

Ball Gage: The prescribed small amount by which the lot mean diameter should differ form nominal diameter, this amount being one of an established series of amounts. A ball gage, in combination with the ball grade and nominal ball diameter should be considered as the most exact ball size specification to be used by a customer for ordering purposes.

Nominal Ball Diameter: The diameter value that is used for the purpose of general identification of a ball size, e.g. 1/4", 6mm, etc.

Nominal Ball Diameter Tolerance: The maximum allowable deviation of any ball by a specific indenting shape.

Specific Diameter: The mount by which the lot mean diameter differs from the nominal diameter, accurate to the container marking increment for that grade.  The specific diameter should be marked on the unit container.

Container Marking Increment: The standard unit steps in micrometers or in microinches, used to express the specific diameter.

Hardness: The measure of resistance to penetration of the ball surface or truncated flat of the ball by a specific indenting shape.

Surface Roughness: Surface roughness consist of all those irregularities which form surface relief and which are conventionally defined within the area where deviations of form and waviness are eliminated. Determined by a stylus type instrument with the ball rotating.  Compliance with Ra limits specific in ABMA Std. 10.

Waviness: The more widely spaced circumferential component of surface texture.