---
type: "fit-designation"
designation: "d9"
letter: "d"
it_grade: "ITIT9"
feature: "shaft"
role: "Free running shaft where accuracy is not essential."
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/d9
---

# d9 Tolerance — ISO 286 Shaft Limits by Nominal Size

A 25 mm d9 shaft runs 24.883 to 24.935 mm — deviations -117 to -65 µm on a 52 µm band. d9 is the ISO 286 shaft tolerance built from fundamental deviation d and standard tolerance grade ITIT9. Free running shaft where accuracy is not essential.

- **Designation**: d9
- **Feature**: shaft
- **Fundamental deviation**: d — Free running clearance
- **Tolerance grade**: ITIT9
- **Typical use**: Free running shaft where accuracy is not essential.
- **Standard**: ISO 286-1:2010, ISO 286-2:2010

## d9 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 | -30 | -60 | 4.940 | 4.970 | 30 |
| 6 mm | -30 | -60 | 5.940 | 5.970 | 30 |
| 8 mm | -40 | -76 | 7.924 | 7.960 | 36 |
| 10 mm | -40 | -76 | 9.924 | 9.960 | 36 |
| 12 mm | -50 | -93 | 11.907 | 11.950 | 43 |
| 16 mm | -50 | -93 | 15.907 | 15.950 | 43 |
| 20 mm | -65 | -117 | 19.883 | 19.935 | 52 |
| 25 mm | -65 | -117 | 24.883 | 24.935 | 52 |
| 30 mm | -65 | -117 | 29.883 | 29.935 | 52 |
| 40 mm | -80 | -142 | 39.858 | 39.920 | 62 |
| 50 mm | -80 | -142 | 49.858 | 49.920 | 62 |
| 80 mm | -100 | -174 | 79.826 | 79.900 | 74 |
| 100 mm | -120 | -207 | 99.793 | 99.880 | 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 d9

### d9 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 d9 Tolerance

### What is an d9 tolerance?

d9 is an ISO 286 shaft tolerance: fundamental deviation d at IT grade IT9. Free running shaft where accuracy is not essential. Free running clearance describes what the d deviation does.

### What is the tolerance on a 25 mm d9 shaft?

A 25 mm d9 shaft runs 24.883 to 24.935 mm — deviations -117 to -65 µm, a tolerance band of 52 µm.

## Fits Built on d9

Standard hole/shaft pairs that use d9 as their shaft.

| Fit | Classification | Basis | Typical use |
| --- | --- | --- | --- |
| [H9/d9](https://shopmath.org/fits/h9-d9.md) | Clearance | hole basis | Free running. Good where accuracy is not essential and clearance can be generous. |

## 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)

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*Source: [ShopMath](https://shopmath.org/fits/d9) — data verified August 1, 2026. Reference data; verify against the governing standard before manufacture.*