---
type: "fit-size"
designation: "g6"
nominal_size_mm: 20
feature: "shaft"
letter: "g"
it_grade: "ITIT6"
upper_deviation_um: -7
lower_deviation_um: -20
min_dia_mm: 19.98
max_dia_mm: 19.993
it_tolerance_um: 13
standard: "ISO 286-1:2010, ISO 286-2:2010"
verified: "August 1, 2026"
url: https://shopmath.org/fits/g6/20mm
---

# 20 mm g6 Tolerance — Limits, Deviations and Band

A 20 mm g6 shaft runs 19.980 to 19.993 mm — deviations -20 to -7 µm from nominal, on an ITIT6 band of 13 µm. Sliding shaft with minimal clearance — locates accurately and still moves freely.

- **Designation**: g6 at 20 mm
- **Feature**: shaft
- **Upper limit**: 19.993 mm (-7 µm)
- **Lower limit**: 19.980 mm (-20 µm)
- **Tolerance band**: 13 µm (ITIT6)
- **Fundamental deviation**: g — Sliding, small clearance
- **Standard**: ISO 286-1:2010, ISO 286-2:2010

## 20 mm g6 Limits

| Property | Micrometres | Millimetres |
| --- | --- | --- |
| Upper deviation | -7 | -0.007 |
| Lower deviation | -20 | -0.020 |
| Tolerance band (IT) | 13 | 0.013 |
| Maximum diameter |  | 19.993 |
| Minimum diameter |  | 19.980 |

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

## Other Standard Tolerances at 20 mm

The other ISO 286 designations that carry a page at 20 mm — the comparison to make when g6 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/f7/20mm.md) | shaft | -41 | -20 | 19.959 | 19.980 | 21 |
| [h6](https://shopmath.org/fits/h6/20mm.md) | shaft | -13 | +0 | 19.987 | 20.000 | 13 |
| [H7](https://shopmath.org/fits/h7/20mm.md) | hole | +0 | +21 | 20.000 | 20.021 | 21 |
| [h7](https://shopmath.org/fits/h7-shaft/20mm.md) | shaft | -21 | +0 | 19.979 | 20.000 | 21 |
| [p6](https://shopmath.org/fits/p6/20mm.md) | shaft | +22 | +35 | 20.022 | 20.035 | 13 |

## ISO 286 Standard Tolerance Grades at 20 mm

Every IT grade in the size band 20 mm falls in. The letter sets where the band sits; the IT grade sets how wide it is.

| Grade | Tolerance (µm) | Tolerance (mm) |
| --- | --- | --- |
| IT5 | 9 | 0.009 |
| IT6 | 13 | 0.013 |
| IT7 | 21 | 0.021 |
| IT8 | 33 | 0.033 |
| IT9 | 52 | 0.052 |
| IT10 | 84 | 0.084 |
| IT11 | 130 | 0.130 |
| IT12 | 210 | 0.210 |

## Sources and Method for 20 mm g6

### g6 at 20 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 20 mm g6

### What is the tolerance for a 20 mm g6 shaft?

A 20 mm g6 shaft is 19.980 to 19.993 mm — deviations -20 to -7 µm from nominal, a total tolerance band of 13 µm.

### What size reamer or bore does a 20 mm g6 shaft need?

Aim for the middle of the band: 19.986 mm, with 13 µm of total spread available between 19.980 and 19.993 mm.

### How much is 13 µm in millimetres and inches?

13 µm is 0.013 mm, or 0.00051 in.

## Related pages

- Smaller size: [16 mm g6](https://shopmath.org/fits/g6/16mm.md)
- Larger size: [25 mm g6](https://shopmath.org/fits/g6/25mm.md)
- All sizes of this tolerance: [g6 limits by size](https://shopmath.org/fits/g6.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/g6/20mm) — data verified August 1, 2026. Reference data; verify against the governing standard before manufacture.*