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.
