What is the H7 tolerance for a 25 mm bore?

Zero to +0.021 mm. The 25 mm bore falls in the 18–30 mm size range, where IT7 is 21 µm, and an H hole starts at nominal and extends upward by the grade. So the bore may measure 25.000 to 25.021 mm.

What is the h6 tolerance for a 25 mm shaft?

Zero to −0.013 mm — the shaft may measure 24.987 to 25.000 mm. The 25 mm shaft falls in the 18–30 mm range where IT6 is 13 µm, and an h shaft starts at nominal and extends downward.

What is the clearance of an H7/h6 fit?

Between 0 and the sum of the two tolerances. At 25 mm that is 0 to 0.034 mm. The minimum is always zero because both parts can be made at exactly nominal, which is what makes it a clearance fit that locates well and still assembles by hand.

Why is H7/h6 so common?

Because it gives zero minimum clearance — the tightest location a clearance fit can give — while still assembling without a press. It is the default for covers, spigots, bolted joints and any part located by the fit but held by fasteners.

Why are only H7 and h6 in this table?

Because those two tolerance zone positions are defined by rule — H starts at nominal and goes up, h starts at nominal and goes down — so they can be derived from the IT grades. Every other letter has a fundamental deviation that must be looked up in ISO 286-2.

Hole and Shaft Limits (H7 / h6)

Limit deviations for the H7 hole and the h6 shaft at every ISO 286 size range, with the clearance range the pairing produces.

Data verified 2026-09-29 · based on ISO 286-1:2010

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H7 / h6 Limit Deviations by Nominal Size

Nominal size mm^[4]	IT6 µm^[4]	h6 shaft limits mm^[3]	IT7 µm^[4]	H7 hole limits mm^[1]	Max clearance mm^[2]	Max clearance in^[2]
0–3 #	6	0 / −0.006	10	0 / +0.010	0.016	0.00063
3–6 #	8	0 / −0.008	12	0 / +0.012	0.020	0.000787
6–10 #	9	0 / −0.009	15	0 / +0.015	0.024	0.000945
10–18 #	11	0 / −0.011	18	0 / +0.018	0.029	0.00114
18–30 #	13	0 / −0.013	21	0 / +0.021	0.034	0.00134
30–50 #	16	0 / −0.016	25	0 / +0.025	0.041	0.00161
50–80 #	19	0 / −0.019	30	0 / +0.030	0.049	0.00193
80–120 #	22	0 / −0.022	35	0 / +0.035	0.057	0.00224
120–180 #	25	0 / −0.025	40	0 / +0.040	0.065	0.00256
180–250 #	29	0 / −0.029	46	0 / +0.046	0.075	0.00295
250–315 #	32	0 / −0.032	52	0 / +0.052	0.084	0.00331
315–400 #	36	0 / −0.036	57	0 / +0.057	0.093	0.00366
400–500 #	40	0 / −0.040	63	0 / +0.063	0.103	0.00406

Both rows are derivable, which is why they are reliable. By definition an H hole has its lower deviation at zero and extends upward by the IT grade, and an h shaft has its upper deviation at zero and extends downward — so the two limit columns follow directly from the IT table and need no separate deviation table.

The minimum clearance of H7/h6 is always zero, and the maximum is IT7 + IT6, because the hole can be at its largest while the shaft is at its smallest. That zero minimum is what makes H7/h6 the most-used fit in general engineering: it locates the part as well as a clearance fit can and still assembles by hand.

Other letters are not covered here. For g6, f7, k6, p6, s6 and the rest, the fundamental deviation sets where the tolerance zone sits, and those values come from the ISO 286-2 tables rather than from a rule. Use the fits and tolerances chart to choose the fit, and ISO 286-2 for its numerical deviations.

Reading a Fit from Its Limits

Take a 25 mm shaft and bore specified as 25H7/h6. From the table, the 18–30 mm row gives an IT7 of 21 µm and an IT6 of 13 µm, so:

The hole is 25.000 to 25.021 mm (H7: zero to +21 µm). The shaft is 24.987 to 25.000 mm (h6: −13 µm to zero). The clearance therefore ranges from 0 — when the hole is at 25.000 and the shaft at 25.000 — to 0.034 mm when the hole is at its largest and the shaft at its smallest.

That clearance range is what the fit actually delivers. A 0.034 mm maximum on a 25 mm diameter is a loose-ish location: the part can sit up to 34 µm off centre. Where that is too much, H7/g6 or H7/h5 tightens it; where it is too little for assembly with a rough surface finish, H7/f7 or H7/e8 loosens it.

Note that these are limits of size. Roundness, taper and surface roughness all consume part of the clearance in practice, which is why a fit calculated at zero minimum clearance needs the surfaces to be geometrically good. On a turned surface at the edge of its size tolerance, the effective clearance can be negative even though the size calculation says otherwise.

Frequently Asked Questions

What is the H7 tolerance for a 25 mm bore?: Zero to +0.021 mm. The 25 mm bore falls in the 18–30 mm size range, where IT7 is 21 µm, and an H hole starts at nominal and extends upward by the grade. So the bore may measure 25.000 to 25.021 mm.
What is the h6 tolerance for a 25 mm shaft?: Zero to −0.013 mm — the shaft may measure 24.987 to 25.000 mm. The 25 mm shaft falls in the 18–30 mm range where IT6 is 13 µm, and an h shaft starts at nominal and extends downward.
What is the clearance of an H7/h6 fit?: Between 0 and the sum of the two tolerances. At 25 mm that is 0 to 0.034 mm. The minimum is always zero because both parts can be made at exactly nominal, which is what makes it a clearance fit that locates well and still assembles by hand.
Why is H7/h6 so common?: Because it gives zero minimum clearance — the tightest location a clearance fit can give — while still assembling without a press. It is the default for covers, spigots, bolted joints and any part located by the fit but held by fasteners.
Why are only H7 and h6 in this table?: Because those two tolerance zone positions are defined by rule — H starts at nominal and goes up, h starts at nominal and goes down — so they can be derived from the IT grades. Every other letter has a fundamental deviation that must be looked up in ISO 286-2.

Value Sources

Each data column on this page is tied to the source it came from. The numbers in square brackets correspond to the table headers above.

#	Source	Type	Revision / method
[1]	Value computed from the standard's defining relationship	derived	Computed at build time from the defining relationship and verified against every row.
[2]	Value computed from the standard's defining relationship	derived	Computed at build time from the defining relationship and verified against every row.
[3]	Value computed from the standard's defining relationship	derived	Computed at build time from the defining relationship and verified against every row.
[4]	ISO 286-1 — ISO code system for tolerances on linear sizes: basis of tolerances, deviations and fits	standard	ISO 286-1:2010
[5]	ISO 286-2 — Tables of standard tolerance grades and limit deviations for holes and shafts	standard	ISO 286-2:2010

Data Sources

Standard	Revision	What it covers on this page
ISO 286-1 — Basis of tolerances, deviations and fits	ISO 286-1:2010	the IT grade values and the H and h zone positions
ISO 286-2 — Tables of standard tolerance grades and limit deviations	ISO 286-2:2010	the fundamental deviations for letters other than H and h
ISO 286-1 Annex — Graphical representation of the ISO code system	ISO 286-1:2010	how the tolerance zones are positioned relative to nominal

Cross-checked against:

The IT grade values checked against the ISO 286 tolerance chart on this site, so the two pages cannot disagree
Both limit columns derived from the defining rule (H up from nominal, h down from nominal) and recomputed at build time
The maximum clearance verified as the sum of the two IT grades on every row
Five values held as known-value checks including two derived clearances

Derived values — the following values on this page are calculated, not taken directly from the standard:

Value	How it is derived
h6 and H7 limit deviations	By definition h = 0 to −IT6 and H = 0 to +IT7. Both follow directly from the ISO 286 IT grades with no separate deviation table needed.
Minimum and maximum clearance	Minimum = 0 always, since both parts may be made at nominal. Maximum = (IT6 + IT7) ÷ 1000 mm, recomputed and verified at build time on every row.

The table covers H7 and h6 only, because those zone positions are defined by rule. Other deviation letters require the ISO 286-2 tables. Limit deviations are sizes — roundness, taper and surface finish consume part of the clearance in service, so a fit at zero minimum clearance needs geometrically good surfaces.

Accuracy and use. The values on this page are compiled from the published standards and cross-checked sources listed above. Where values are derived, the derivation is stated. No warranty, express or implied, is made as to the accuracy or completeness of this information, and no liability is accepted for any loss or damage arising from its use. Engineering reference data is provided for guidance in preliminary work — before a value is used for design, fabrication or acceptance testing, verify it against the current revision of the governing standard and against your own inspection. The user assumes all risk and responsibility in connection with the use of this information.

Cite This Page

Every value on this page is traceable to the sources listed above. If you use the data in a document, paper or report, cite it as:

Plain text

Engineering Reference. "Hole and Shaft Limits (H7 / h6)." https://refmanual.com/charts/hole-shaft-limits/ (accessed 2026-09-29). Data from ISO 286-1 — Basis of tolerances, deviations and fits, ISO 286-1:2010.

BibTeX

@misc{hole-shaft-limits,
  title        = {Hole and Shaft Limits (H7 / h6)},
  author       = {{Engineering Reference}},
  howpublished = {\url{https://refmanual.com/charts/hole-shaft-limits/}},
  note         = {Accessed: 2026-09-29},
  source       = {ISO 286-1 — Basis of tolerances, deviations and fits, ISO 286-1:2010}
}

RIS (EndNote, Zotero, Mendeley)

TY  - ELEC
TI  - Hole and Shaft Limits (H7 / h6)
AU  - Engineering Reference
PB  - Engineering Reference
UR  - https://refmanual.com/charts/hole-shaft-limits/
PY  - 2026
DA  - 2026-09-29
N1  - Source: ISO 286-1 — Basis of tolerances, deviations and fits, ISO 286-1:2010
ER  -

Each row in the tables above also has a permanent link — hover a row and use the # link to cite a single value rather than the whole page.