| Roughness values Ra | Roughness values Ra | Roughness |
| micrometers | microinches | Grade Numbers |
| 50 | 2000 | N12 |
| 25 | 1000 | N11 |
| 12.5 | 500 | N10 |
| 6.3 | 250 | N9 |
| 3.2 | 125 | N8 |
| 1.6 | 63 | N7 |
| 0.8 | 32 | N6 |
| 0.4 | 16 | N5 |
| 0.2 | 8 | N4 |
| 0.1 | 4 | N3 |
| 0.05 | 2 | N2 |
| 0.025 | 1 | N1 |
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| Roughness values Ra | Roughness values Ra | Roughness |
| micrometers | microinches | Grade Numbers |
| 50 | 2000 | N12 |
| 25 | 1000 | N11 |
| 12.5 | 500 | N10 |
| 6.3 | 250 | N9 |
| 3.2 | 125 | N8 |
| 1.6 | 63 | N7 |
| 0.8 | 32 | N6 |
| 0.4 | 16 | N5 |
| 0.2 | 8 | N4 |
| 0.1 | 4 | N3 |
| 0.05 | 2 | N2 |
| 0.025 | 1 | N1 |