Read an existing label
Use this table to interpret an old N label, then confirm its drawing context. The table is a published comparator-product reference, not a statement that every sample has exactly the nominal value.
Do not turn a measurement into automatic acceptance
A measured Ra of 1.7 µm must not be rounded into N7 or N8 and declared acceptable. Use the actual limit and acceptance rules on the drawing. The listed values are not generated by exact successive doubling.
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| Legacy label | Ra · µm | Ra · µin |
|---|---|---|
| N1 | 0.025 | 0.984251969 |
| N2 | 0.05 | 1.96850394 |
| N3 | 0.1 | 3.93700787 |
| N4 | 0.2 | 7.87401575 |
| N5 | 0.4 | 15.7480315 |
| N6 | 0.8 | 31.496063 |
| N7 | 1.6 | 62.992126 |
| N8 | 3.2 | 125.984252 |
| N9 | 6.3 | 248.031496 |
| N10 | 12.5 | 492.125984 |
| N11 | 25 | 984.251969 |
| N12 | 50 | 1968.50394 |
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Sources and review scope
Reviewed 23 October 2026. Arithmetic examples are labelled separately from source-table facts and standard scope.
MISUMI / Nihon Kinzoku Denchu Ra comparator reference
Selection support table: N1–N12 nominal Ra values, referencing JIS B 0659-1:2002 Annex 1. Comparator product reference, not workpiece acceptance limits.
Open the original source ↗NIST SI Units — Length
International inch definition: exactly 25.4 mm. Other unit values on these pages are derived arithmetic.
Open the original source ↗