Roughness Average (Ra)
The Roughness Average Ra is a common way to express the surface finish, however it can refer to both metric and imperial units. Grit is literally the size of the grit required to achieve a certain surface finish during sand blasting.
Imperial Ra is stated in micron inches (µIn) or Grit.
Metric Ra is stated in micron meters (µm).
µIn x .025 = µm
µm x 40 = µIn
| Description | Grit (US) | µIn | µm |
|---|---|---|---|
| Ultra High Purity Electropolished | 320 = (10-19 µIn Ra) | 10 | 0.25 |
| Sanitary Electropolished (3A) | 240= (20-29 µIn Ra) | 20 | 0.5 |
| Mechanical Polish Standard | 180= (30-39 µIn Ra) | 40 | 1 |
