A.F.B.M.A. Ball Grades and Standard Sizes

A.F.B.M.A. Grades Diameter Tolerance (µm) Diameter Tolerance (inches) Lot Diameter Variation (µm) Lot Diameter Variation (inches) Basic Diameter Tolerance (µm) Basic Diameter Tolerance (inches) Surface Roughness Ra (µm) Surface Roughness Ra (inches)
5 0.125 0.000005 ±0.15 ±0.000006 ±1.0 ±0.00004 0.008 ±0.0000003
10 0.250 0.000010 ±0.25 ±0.000010 ±2.5 ±0.00010 0.010 ±0.0000004
15 0.375 0.000015 ±0.40 ±0.000015 ±2.5 ±0.00010 0.010 ±0.0000004
25 0.625 0.000025 ±0.70 ±0.000025 ±2.5 ±0.00010 0.010 ±0.0000004
50 1.250 0.000050 ±1.25 ±0.000050 ±5.0 ±0.00020 0.020 ±0.0000008
100 2.500 0.000100 ±2.50 ±0.000100 ±10.0 ±0.00040 0.020 ±0.0000015

A.F.B.M.A. Grades – Measure of the degree of precision with respect to key functional characteristics. Lower grade number indicates greater precision.
Diameter Tolerance per Ball – The permissible difference between the largest and smallest diameter measurable on one ball.
Lot Diameter Variation – The permissible range of the average diameters of the individual balls within any one lot.
Basic Diameter Tolerance – The maximum allowable deviation of any ball diameter from the basic diameter within a shipment.