---
type: "fit-size"
designation: "h6"
nominal_size_mm: 40
feature: "shaft"
letter: "h"
it_grade: "ITIT6"
upper_deviation_um: 0
lower_deviation_um: -16
min_dia_mm: 39.984
max_dia_mm: 40
it_tolerance_um: 16
standard: "ISO 286-1:2010, ISO 286-2:2010"
verified: "August 1, 2026"
url: https://shopmath.org/fits/h6/40mm
---

# 40 mm h6 Tolerance — Limits, Deviations and Band

A 40 mm h6 shaft runs 39.984 to 40.000 mm — deviations -16 to +0 µm from nominal, on an ITIT6 band of 16 µm. Precision basic shaft — zero upper deviation, the reference for locational clearance fits.

- **Designation**: h6 at 40 mm
- **Feature**: shaft
- **Upper limit**: 40.000 mm (+0 µm)
- **Lower limit**: 39.984 mm (-16 µm)
- **Tolerance band**: 16 µm (ITIT6)
- **Fundamental deviation**: h — Zero deviation — the basic shaft
- **Standard**: ISO 286-1:2010, ISO 286-2:2010

## 40 mm h6 Limits

| Property | Micrometres | Millimetres |
| --- | --- | --- |
| Upper deviation | +0 | 0.000 |
| Lower deviation | -16 | -0.016 |
| Tolerance band (IT) | 16 | 0.016 |
| Maximum diameter |  | 40.000 |
| Minimum diameter |  | 39.984 |

_Deviations are measured from the nominal size. A diameter outside the two limits is a reject._

## Other Standard Tolerances at 40 mm

The other ISO 286 designations that carry a page at 40 mm — the comparison to make when h6 is the wrong fit.

| Designation | Feature | Lower deviation (µm) | Upper deviation (µm) | Min Ø (mm) | Max Ø (mm) | IT band (µm) |
| --- | --- | --- | --- | --- | --- | --- |
| [f7](https://shopmath.org/fits/f7/40mm.md) | shaft | -50 | -25 | 39.950 | 39.975 | 25 |
| [g6](https://shopmath.org/fits/g6/40mm.md) | shaft | -25 | -9 | 39.975 | 39.991 | 16 |
| [H7](https://shopmath.org/fits/h7/40mm.md) | hole | +0 | +25 | 40.000 | 40.025 | 25 |
| [h7](https://shopmath.org/fits/h7-shaft/40mm.md) | shaft | -25 | +0 | 39.975 | 40.000 | 25 |
| [p6](https://shopmath.org/fits/p6/40mm.md) | shaft | +26 | +42 | 40.026 | 40.042 | 16 |

## ISO 286 Standard Tolerance Grades at 40 mm

Every IT grade in the size band 40 mm falls in. The letter sets where the band sits; the IT grade sets how wide it is.

| Grade | Tolerance (µm) | Tolerance (mm) |
| --- | --- | --- |
| IT5 | 11 | 0.011 |
| IT6 | 16 | 0.016 |
| IT7 | 25 | 0.025 |
| IT8 | 39 | 0.039 |
| IT9 | 62 | 0.062 |
| IT10 | 100 | 0.100 |
| IT11 | 160 | 0.160 |
| IT12 | 250 | 0.250 |

## Sources and Method for 40 mm h6

### h6 at 40 mm

- **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.
- ISO 286 tabulates per size band, so this value holds across the band the nominal size falls in.
- 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 40 mm h6

### What is the tolerance for a 40 mm h6 shaft?

A 40 mm h6 shaft is 39.984 to 40.000 mm — deviations -16 to +0 µm from nominal, a total tolerance band of 16 µm.

### What size reamer or bore does a 40 mm h6 shaft need?

Aim for the middle of the band: 39.992 mm, with 16 µm of total spread available between 39.984 and 40.000 mm.

### How much is 16 µm in millimetres and inches?

16 µm is 0.016 mm, or 0.00063 in.

## Related pages

- Smaller size: [30 mm h6](https://shopmath.org/fits/h6/30mm.md)
- Larger size: [50 mm h6](https://shopmath.org/fits/h6/50mm.md)
- All sizes of this tolerance: [h6 limits by size](https://shopmath.org/fits/h6.md)
- 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/h6/40mm) — data verified August 1, 2026. Reference data; verify against the governing standard before manufacture.*