ABMA Standards

Grade

The precision of a steel ball is indicated by a number; smaller numbers indicate greater precision.

Basic Diameter

The basic diameter, used to distinguish steel ball sizes, is determined by measuring the distance between two parallel surfaces in contact with the ball.

Average Diameter

The arithmetic average of the maximum and minimum diameters of a steel ball.

Batch Average Diameter

The arithmetic average of the average diameters of the largest and smallest steel balls within a production batch.

Batch Diameter Tolerance

The difference between the average diameters of the largest and smallest steel balls within a production batch.

Diameter Tolerance

The difference between the maximum and minimum diameters of a single ball.

Roundness

The maximum difference between the radial distance of the smallest spherical surface and the radial distance of each point on the ball's surface is the ball's true roundness.

Surface Roughness

Different grades of steel balls have different surface roughness ranges. Please refer to the Grade and Tolerance Table.

Hardness

Two testing methods are available: spherical hardness and flat hardness. Please refer to the Hardness and Crush Value Table.

Carburization

The distance from the steel ball surface to the center point with a hardness of RC 50 is the carburizing depth. This is only applicable to heat-treatable steels.

UNIT

VDS

W

VDL

Ra

3

0.08

0.08

0.16

0.010

5

0.13

0.13

0.25

0.014

10

0.25

0.25

0.50

0.020

20

0.5

0.5

1.0

0.032

40

1.0

1.0

2.0

0.06

60

1.5

1.5

3.0

0.08

80

2.0

2.0

4.0

0.1

100

2.5

2.5

5.0

0.1

200

5.0

5.0

10

0.15

300

7.5

7.5

15

×

500

12.5

12.5

25

×

800

20

20

40

×

1000

25

25

50

×

2000

50

50

100

×