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Bearing Ball Grade Chart

Grade

Deviation from
Spherical Form

Lot Diameter
Variation

Nominal Ball
Diameter Tolerance

Maximum Surface
Roughness in
Micro inches "Ra"

5

0.000005

±0.000005

±0.00003

0.8

10

0.00001

±0.000010

±0.0001

1.0

25

0.000025

±0.000025

±00.0001

2.0

50

0.00005

±0.000050

±0.0002

3.0

100

0.0001

±0.0001

±0.0005

5.0

200

0.0002

±0.0002

±0.001

8.0

1000

0.001

±0.001

±0.005

 

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

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

Nominal Ball Diameter: The diameter value that is used for the purpose of general identification of a ball size

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. 

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