---
type: "fit-designation"
designation: "n6"
letter: "n"
it_grade: "ITIT6"
feature: "shaft"
role: "Tight transition shaft — usually needs a press for assembly."
size_count: 13
size_range_mm: "5–100"
standard: "ISO 286-1:2010, ISO 286-2:2010"
verified: "August 1, 2026"
url: https://shopmath.org/fits/n6
---

# n6 Tolerance — ISO 286 Shaft Limits by Nominal Size

A 25 mm n6 shaft runs 25.015 to 25.028 mm — deviations +15 to +28 µm on a 13 µm band. n6 is the ISO 286 shaft tolerance built from fundamental deviation n and standard tolerance grade ITIT6. Tight transition shaft — usually needs a press for assembly.

- **Designation**: n6
- **Feature**: shaft
- **Fundamental deviation**: n — Tight transition
- **Tolerance grade**: ITIT6
- **Typical use**: Tight transition shaft — usually needs a press for assembly.
- **Standard**: ISO 286-1:2010, ISO 286-2:2010

## n6 Limits and Deviations by Nominal Size

Deviations are in micrometres from the nominal size; limits are the finished diameters in millimetres. Sizes that carry their own page are linked.

| Nominal size | Upper deviation (µm) | Lower deviation (µm) | Min shaft Ø (mm) | Max shaft Ø (mm) | IT tolerance (µm) |
| --- | --- | --- | --- | --- | --- |
| 5 mm | +16 | +8 | 5.008 | 5.016 | 8 |
| 6 mm | +16 | +8 | 6.008 | 6.016 | 8 |
| 8 mm | +19 | +10 | 8.010 | 8.019 | 9 |
| 10 mm | +19 | +10 | 10.010 | 10.019 | 9 |
| 12 mm | +23 | +12 | 12.012 | 12.023 | 11 |
| 16 mm | +23 | +12 | 16.012 | 16.023 | 11 |
| 20 mm | +28 | +15 | 20.015 | 20.028 | 13 |
| 25 mm | +28 | +15 | 25.015 | 25.028 | 13 |
| 30 mm | +28 | +15 | 30.015 | 30.028 | 13 |
| 40 mm | +33 | +17 | 40.017 | 40.033 | 16 |
| 50 mm | +33 | +17 | 50.017 | 50.033 | 16 |
| 80 mm | +39 | +20 | 80.020 | 80.039 | 19 |
| 100 mm | +45 | +23 | 100.023 | 100.045 | 22 |

_ISO 286 tabulates deviations per size band, so a value holds across the whole band a nominal size falls in, not just at that exact diameter._

## Sources and Method for n6

### n6 deviations

- **Source**: limits computed from the compiled ISO 286 tables: ISO 286-1 IT grades and ISO 286-2 fundamental deviations, compiled from saucecode/ISO286 (LGPL-2.1) and parkergreene/isofits (MIT), cross-checked cell-for-cell
- **Method**: computed
- **Verified against**: parkergreene/isofits ISO 286-2 limit tables (MIT); ISO 286-1 formula harness — 2067 checks passed

### Assumptions

- Values are the ISO 286-2 tabulated limits, not the ISO 286-1 formula: the formula deviates from the table by up to 13.26% and is carried only as a validation harness.
- Limits are at 20 °C, the ISO 1 reference temperature.
- Dataset scope: COMPILED not computed: the ISO 286-1 formula deviates up to 13.26% from the table and is used only as a harness (warn >5%, fail >15%). EXCLUDED: shaft/hole letters s, t, u and the fits H7/s6, H7/t6, H7/u6 — no free source and an undetermined step constant in the formula.

**Data last verified**: August 1, 2026

## Common Questions About the n6 Tolerance

### What is an n6 tolerance?

n6 is an ISO 286 shaft tolerance: fundamental deviation n at IT grade IT6. Tight transition shaft — usually needs a press for assembly. Tight transition describes what the n deviation does.

### What is the tolerance on a 25 mm n6 shaft?

A 25 mm n6 shaft runs 25.015 to 25.028 mm — deviations +15 to +28 µm, a tolerance band of 13 µm.

## Fits Built on n6

Standard hole/shaft pairs that use n6 as their shaft.

| Fit | Classification | Basis | Typical use |
| --- | --- | --- | --- |
| [H7/n6](https://shopmath.org/fits/h7-n6.md) | Transition | hole basis | Tight transition. Usually a press job. |

## Related pages

- All fits and tolerances: [ISO 286 fit reference](https://shopmath.org/fits.md)
- Full grade table: [ISO 286 tolerance chart](https://shopmath.org/charts/iso-tolerances.md)

---

*Source: [ShopMath](https://shopmath.org/fits/n6) — data verified August 1, 2026. Reference data; verify against the governing standard before manufacture.*