---
type: "fit-designation"
designation: "H8"
letter: "H"
it_grade: "ITIT8"
feature: "hole"
role: "Basic hole where a close running fit is wanted but H7 is more precision than the job needs."
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/h8
---

# H8 Tolerance — ISO 286 Hole Limits by Nominal Size

A 25 mm H8 hole runs 25.000 to 25.033 mm — deviations +0 to +33 µm on a 33 µm band. H8 is the ISO 286 hole tolerance built from fundamental deviation H and standard tolerance grade ITIT8. Basic hole where a close running fit is wanted but H7 is more precision than the job needs.

- **Designation**: H8
- **Feature**: hole
- **Fundamental deviation**: H — Zero deviation — the basic hole
- **Tolerance grade**: ITIT8
- **Typical use**: Basic hole where a close running fit is wanted but H7 is more precision than the job needs.
- **Standard**: ISO 286-1:2010, ISO 286-2:2010

## H8 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 hole Ø (mm) | Max hole Ø (mm) | IT tolerance (µm) |
| --- | --- | --- | --- | --- | --- |
| 5 mm | +18 | +0 | 5.000 | 5.018 | 18 |
| 6 mm | +18 | +0 | 6.000 | 6.018 | 18 |
| 8 mm | +22 | +0 | 8.000 | 8.022 | 22 |
| 10 mm | +22 | +0 | 10.000 | 10.022 | 22 |
| 12 mm | +27 | +0 | 12.000 | 12.027 | 27 |
| 16 mm | +27 | +0 | 16.000 | 16.027 | 27 |
| 20 mm | +33 | +0 | 20.000 | 20.033 | 33 |
| 25 mm | +33 | +0 | 25.000 | 25.033 | 33 |
| 30 mm | +33 | +0 | 30.000 | 30.033 | 33 |
| 40 mm | +39 | +0 | 40.000 | 40.039 | 39 |
| 50 mm | +39 | +0 | 50.000 | 50.039 | 39 |
| 80 mm | +46 | +0 | 80.000 | 80.046 | 46 |
| 100 mm | +54 | +0 | 100.000 | 100.054 | 54 |

_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 H8

### H8 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 H8 Tolerance

### What is an H8 tolerance?

H8 is an ISO 286 hole tolerance: fundamental deviation H at IT grade IT8. Basic hole where a close running fit is wanted but H7 is more precision than the job needs. Zero deviation — the basic hole describes what the H deviation does.

### What is the tolerance on a 25 mm H8 hole?

A 25 mm H8 hole runs 25.000 to 25.033 mm — deviations +0 to +33 µm, a tolerance band of 33 µm.

## Fits Built on H8

Standard hole/shaft pairs that use H8 as their hole.

| Fit | Classification | Basis | Typical use |
| --- | --- | --- | --- |
| [H8/e8](https://shopmath.org/fits/h8-e8.md) | Clearance | hole basis | Running fit with room for a lubricant film at speed. |
| [H8/f7](https://shopmath.org/fits/h8-f7.md) | Clearance | hole basis | Close running. The general-purpose lubricated journal fit. |

## 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/h8) — data verified August 1, 2026. Reference data; verify against the governing standard before manufacture.*