---
type: "fit-designation"
designation: "h9"
letter: "h"
it_grade: "ITIT9"
feature: "shaft"
role: "Basic shaft for shaft-basis free running fits."
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/h9-shaft
---

# h9 Tolerance — ISO 286 Shaft Limits by Nominal Size

A 25 mm h9 shaft runs 24.948 to 25.000 mm — deviations -52 to +0 µm on a 52 µm band. h9 is the ISO 286 shaft tolerance built from fundamental deviation h and standard tolerance grade ITIT9. Basic shaft for shaft-basis free running fits.

- **Designation**: h9
- **Feature**: shaft
- **Fundamental deviation**: h — Zero deviation — the basic shaft
- **Tolerance grade**: ITIT9
- **Typical use**: Basic shaft for shaft-basis free running fits.
- **Standard**: ISO 286-1:2010, ISO 286-2:2010

## h9 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 | +0 | -30 | 4.970 | 5.000 | 30 |
| 6 mm | +0 | -30 | 5.970 | 6.000 | 30 |
| 8 mm | +0 | -36 | 7.964 | 8.000 | 36 |
| 10 mm | +0 | -36 | 9.964 | 10.000 | 36 |
| 12 mm | +0 | -43 | 11.957 | 12.000 | 43 |
| 16 mm | +0 | -43 | 15.957 | 16.000 | 43 |
| 20 mm | +0 | -52 | 19.948 | 20.000 | 52 |
| 25 mm | +0 | -52 | 24.948 | 25.000 | 52 |
| 30 mm | +0 | -52 | 29.948 | 30.000 | 52 |
| 40 mm | +0 | -62 | 39.938 | 40.000 | 62 |
| 50 mm | +0 | -62 | 49.938 | 50.000 | 62 |
| 80 mm | +0 | -74 | 79.926 | 80.000 | 74 |
| 100 mm | +0 | -87 | 99.913 | 100.000 | 87 |

_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 h9

### h9 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 h9 Tolerance

### What is an h9 tolerance?

h9 is an ISO 286 shaft tolerance: fundamental deviation h at IT grade IT9. Basic shaft for shaft-basis free running fits. Zero deviation — the basic shaft describes what the h deviation does.

### What is the tolerance on a 25 mm h9 shaft?

A 25 mm h9 shaft runs 24.948 to 25.000 mm — deviations -52 to +0 µm, a tolerance band of 52 µm.

## 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/h9-shaft) — data verified August 1, 2026. Reference data; verify against the governing standard before manufacture.*