GRADE
  • Grade
    The ball grade (G) is a specific combination of dimensional, form, surface roughness and sorting tolerance for balls. For example, the level of sphericity, expressed in millionths of an inch, e.g., a Grade 10 ball must be round or spherical within 10 millionths of an inch. The grade designation also dictates the other tolerances, per the chart shown below. 
  • Variation of Ball Diameter (VDws)
    Tthe difference between the largest and the smallest of the single diameters of a ball.
  • Variation of Ball Lot Diameter (VDwL)
    The difference between the mean diameters of the largest ball and smallest ball in a ball lot.
  • Ball Lot
    Definite quantity of balls manufactured under conditions presumed uniform and which is considered as an entity.
  • Deviation from Spherical Form
    The difference between the largest and smallest diameters measurable on a single ball. Also referred to as roundness or sphericity.
  • Surface Roughness (Ra)
    Surface irregularities with relatively small spacings, which usually include irregularities resulting from the method of manufacture being used and/or other influences.

Grades (AFBMA) / Tolerances  Chrome and Stainless Steel Balls

Grade (AFBMA) Ball Diameter Tolerance
(Ovality Per Ball)
Basic Diameter Tolerance
(Ball To Ball Variation)
Inches Millimetres Microns Inches Millimetres Microns
20 0.000020 0.0005 0.50 +/- 0.0001 +/- 0.0025 +/- 2.50
25 0.000025 0.0006 0.60 +/- 0.0001 +/- 0.0025 +/- 2.50
100 0.0001 0.0025 2.50 +/- 0.0005 +/- 0.0127 +/- 12.70
200 0.0002 0.0051 5.10 +/- 0.001 +/- 0.0254 +/- 25.40
500 0.0005 0.0127 12.70 +/- 0.002 +/- 0.0508 +/- 50.80
1000 0.001 0.0254 25.40 +/- 0.005 +/- 0.1270 +/- 127
2000 0.002 0.0508 50.80 +/- 0.005 +/- 0.1270 +/

Important Links:

Grades of balls

   No of Balls per /Kg

Burnishing Applications I.S. 2898 (INDIA),I.S.O. 3290 Standard, G.B 308 (G.B)
  How Balls  are made ANSI/AFBMA- (USA),  
    AFNOR NF E 22-381 - (FRANCE)
    DIN 5401 (GERMANY)

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