ISO 286 · H7 hole · Ø20 mm
20 mm H7 Tolerance — Hole Limits in mm and µm
https://shopmath.org/fits/h7/20mm · data verified August 1, 2026
A 20 mm H7 hole is 20.000 to 20.021 mm — deviations of 0 to +21 µm on an IT7 band 21 µm wide. The default basic hole in hole-basis fitting — reamer and gauge sizes are built around it. Values apply at the ISO 286 reference temperature of 20 °C.
- Nominal
- 20 mm
- Designation
- H7
- Feature
- hole
- Grade
- IT7
- Band
- 21 µm
20 mm H7 hole · limits, mm
20.000 … 20.021
- Upper dev
- +21µm
- Lower dev
- 0µm
- Band
- 21µm
Measured at 20 °C on a plain cylindrical feature. The IT7 grade sets the 21 µm width; the H sets where the band sits.
Limits for a 20 mm H7 Hole
Deviations in micrometres, finished limits in millimetres. Both describe the same band — the deviation is what a drawing carries, the limit is what a gauge reads.
| Limit | µm | mm |
|---|---|---|
| Upper deviation | +21 | 0.021 |
| Lower deviation | 0 | 0.000 |
| Maximum diameter | +21 | 20.021 |
| Minimum diameter | 0 | 20.000 |
| Tolerance band (IT7) | 21 | 0.021 |
Deviations are relative to the 20 mm nominal size. Values apply at the ISO 286 reference temperature of 20 °C; a part measured warm is not at these limits.
ISO 286 Tolerance Grades at 20 mm
20 mm falls in the ISO 286 size band over 18 to 30 mm, so every tolerance in that band has the same width regardless of which letter it carries.
| 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 |
The grade sets the width of the band; the letter sets where that band sits relative to the nominal size.
Every Other ISO 286 Tolerance at 20 mm
The same nominal size under every other designation in this reference — the comparison that decides whether a feature is called out H7 or something looser.
| Property | Property | Deviation, µm | Limits, mm | ||
|---|---|---|---|---|---|
| Designation | Applies to | Upper | Lower | Min | Max |
| c11 | shaft | -110 | -240 | 19.760 | 19.890 |
| d9 | shaft | -65 | -117 | 19.883 | 19.935 |
| e8 | shaft | -40 | -73 | 19.927 | 19.960 |
| f7 | shaft | -20 | -41 | 19.959 | 19.980 |
| g6 | shaft | -7 | -20 | 19.980 | 19.993 |
| h11 | shaft | 0 | -130 | 19.870 | 20.000 |
| h6 | shaft | 0 | -13 | 19.987 | 20.000 |
| h7 | shaft | 0 | -21 | 19.979 | 20.000 |
| h9 | shaft | 0 | -52 | 19.948 | 20.000 |
| k6 | shaft | +15 | +2 | 20.002 | 20.015 |
| m6 | shaft | +21 | +8 | 20.008 | 20.021 |
| n6 | shaft | +28 | +15 | 20.015 | 20.028 |
| p6 | shaft | +35 | +22 | 20.022 | 20.035 |
| r6 | shaft | +41 | +28 | 20.028 | 20.041 |
| F8 | hole | +53 | +20 | 20.020 | 20.053 |
| G7 | hole | +28 | +7 | 20.007 | 20.028 |
| H11 | hole | +130 | 0 | 20.000 | 20.130 |
| H6 | hole | +13 | 0 | 20.000 | 20.013 |
| H7 | hole | +21 | 0 | 20.000 | 20.021 |
| H8 | hole | +33 | 0 | 20.000 | 20.033 |
| H9 | hole | +52 | 0 | 20.000 | 20.052 |
| K7 | hole | +6 | -15 | 19.985 | 20.006 |
| N7 | hole | -7 | -28 | 19.972 | 19.993 |
| P7 | hole | -14 | -35 | 19.965 | 19.986 |
Links go to that designation's page for this size where one exists, and to its full size table otherwise.
Standard Fits Available at 20 mm
What each standard hole/shaft pair gives at 20 mm, loosest first. Negative clearance is interference.
| Property | Property | Clearance, µm | Property | |
|---|---|---|---|---|
| Fit | Type | Min | Max | What it is for |
| H7/h6 | clearance | 0 | +34 | Locational clearance. Assembles by hand, no free movement intended. |
| H11/c11 | clearance | +110 | +370 | Loose running. Wide commercial tolerances, large clearance for dirt, paint and thermal growth. |
| H9/d9 | clearance | +65 | +169 | Free running. Good where accuracy is not essential and clearance can be generous. |
| H8/e8 | clearance | +40 | +106 | Running fit with room for a lubricant film at speed. |
| H8/f7 | clearance | +20 | +74 | Close running. The general-purpose lubricated journal fit. |
| H7/g6 | clearance | +7 | +41 | Sliding. Locates accurately, still moves and turns freely. |
| H7/k6 | transition | -15 | +19 | Locational transition. Accurate location, assembles with light force. |
| H7/m6 | transition | -21 | +13 | Locational transition, tighter than k6. |
| H7/n6 | transition | -28 | +6 | Tight transition. Usually a press job. |
| H7/p6 | interference | -35 | -1 | Locational interference. Rigid location in steel without the load capacity of a drive fit. |
| H7/r6 | interference | -41 | -7 | Medium drive. The joint itself carries load. |
| F8/h7 | clearance | +20 | +74 | Close running, shaft basis. |
| G7/h6 | clearance | +7 | +41 | Sliding, shaft basis. The h6 shaft is the reference and the hole carries the clearance. |
| K7/h6 | transition | -15 | +19 | Locational transition, shaft basis. |
| N7/h6 | transition | -28 | +6 | Tight transition, shaft basis. |
| P7/h6 | interference | -35 | -1 | Locational interference, shaft basis. |
Minimum clearance is the largest shaft in the smallest hole; maximum clearance is the smallest shaft in the largest hole.
Sources and Method for the 20 mm H7 Tolerance
- 20 mm H7 limitscomputed
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
Verified against parkergreene/isofits ISO 286-2 limit tables (MIT); ISO 286-1 formula harness — 2067 checks passed
Computed from the standard's formulas, then checked against published tables.
- IT tolerance gradescompiled
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
Verified against parkergreene/isofits ISO 286-2 limit tables (MIT); ISO 286-1 formula harness — 2067 checks passed. Formula per ISO 286-1 standard tolerance factor and fundamental deviation formulas, used as a validation harness only per docs/research/data-sourcing.md §3.6
Compiled from independent public sources that agree cell-for-cell.
- Formula
Limits from the deviations at 20 mm
max Ø = 20 mm + (+21 µm) = 20.021 mm min Ø = 20 mm + (0 µm) = 20.000 mm
The deviations are compiled from the ISO 286-2 tables; the limits are those deviations applied to the nominal size.
- Assumptions
- Values apply at the ISO 286 reference temperature of 20 °C.
- Size only. Form, roundness, cylindricity and surface finish are separate callouts and a part inside these limits can still be unusable without them.
- 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
How to Cite This 20 mm H7 Tolerance Reference
Citation
ShopMath. "20 mm H7 Tolerance — Hole Limits in mm and µm." ShopMath, verified August 1, 2026, https://shopmath.org/fits/h7/20mm
BibTeX
@misc{shopmath-fits-h7-20mm,
title = {20 mm H7 Tolerance — Hole Limits in mm and µm},
author = {{ShopMath}},
year = {2026},
howpublished = {\url{https://shopmath.org/fits/h7/20mm}},
note = {Data verified 2026-08-01}
}Permanent URL
https://shopmath.org/fits/h7/20mm
Common Questions About the 20 mm H7 Tolerance
What is the tolerance for a 20 mm H7 hole?
- A 20 mm H7 hole runs 20.000 to 20.021 mm — deviations of 0 to +21 µm, a band 21 µm wide.
What is the maximum and minimum size of a 20 mm H7 hole?
- Maximum 20.021 mm, minimum 20.000 mm. Anything outside that band is a reject at 20 °C, not a judgement call.
Why is the IT7 band 21 µm at 20 mm?
- Because 20 mm falls in the ISO 286 size band over 18 up to 30 mm, and IT7 is defined per band rather than per size. Every nominal size in that band carries the same 21 µm width for IT7.
What shaft goes in a 20 mm H7 hole?
- At 20 mm the standard pairs run from H7/h6 (0 to +34 µm clearance) through transition to interference fits — the full list with clearances is on this page.
What does the H in H7 mean?
- Zero deviation — the basic hole. It fixes the fundamental deviation — the limit nearest the nominal size — while IT7 fixes the width of the band, which at 20 mm is 21 µm.
All 13 H7 sizes · ISO 286 tolerance chart · Every designation and fit