What Does an ISO 3290 Ball GradeActually Measure?
When engineers specify a precision ball grade such as G10, G16, G28, or G100 under ISO 3290 (DIN 5401 / ANSI/ABMA Std 10), they are defining four critical geometric and surface tolerances rather than the nominal diameter alone:
- Ball Diameter Variation (VDws): The difference between the largest and smallest single diameter measurements on one individual ball.
- Deviation from Spherical Form (tDW): The greatest radial distance in any equatorial plane between a sphere circumscribed around the ball and any point on the ball surface.
- Lot Diameter Variation (VDwl): The difference between the mean diameter of the largest ball and the smallest ball within a single production lot.
- Surface Roughness (Ra): The arithmetic mean deviation of the surface profile, critical for elastohydrodynamic (EHL) lubricant film formation.
ISO 3290 Precision Ball Grade Tolerance Reference Table
| Grade | Sphericity / Dia Variation (µm) | Max Surface Roughness Ra (µm) | Lot Variation (µm) | Typical Industrial Use |
|---|---|---|---|---|
| Grade G3 | 0.08 µm | 0.010 µm | 0.13 µm | Gyroscopes, ultra-high-speed CNC spindles, metrology masters |
| Grade G5 | 0.13 µm | 0.014 µm | 0.25 µm | Aerospace turbines, dental handpieces, precision ball screws |
| Grade G10 | 0.25 µm | 0.020 µm | 0.50 µm | EV traction motors, low-noise deep groove ball bearings |
| Grade G16 | 0.40 µm | 0.025 µm | 0.80 µm | Automotive transmissions, industrial gearboxes, pumps |
| Grade G28 | 0.70 µm | 0.050 µm | 1.40 µm | Agricultural machinery, general bearings, valves |
| Grade G100 | 2.50 µm | 0.125 µm | 5.00 µm | Linear slides, casters, semi-precision mechanisms |
How DSP Verifies Sub-Micron Roundness & Surface Finish
At DSP’s ISO 9001:2015 Quality Assurance Laboratory in Jaipur, every batch of precision balls undergoes Talyrond circular geometry profiling, optical interferometry roughness testing, eddy-current flaw detection, and sub-micron gauge sorting.
Have a drawing requiring tight gauge sorting or custom lapping? Send your specification to our metrology team.