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ISO 286 fits and tolerances

Pick the size and the fit to see hole and shaft limits, the clearance or interference the assembly will get and which preferred fit suits the application.

Pre-sizing and estimating tool: results do not replace design, calculations or reports signed by a licensed professional, nor verification against the applicable codes and standards.

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Size and fit

Deviations come from the ISO 286-1 tables by size range. US inch fits (ANSI B4.1 RC, LC, LT, LN, FN classes) use their own tables; here the ISO fit is applied to the size converted to millimeters.

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Hole and shaft tolerance zones

Deviations from the nominal size (zero line). The gap between bars is clearance; overlap is interference.

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Preferred fits at this size

Range between minimum and maximum clearance of each hole-basis fit. Negative values are interference.

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Preferred fits and applications

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Method, assumptions and references

Equations used

Hole: ES = EI + IT; shaft: es = ei + IT; letters A to H: EI = −es of the lower-case letter; JS and js: ±IT/2
K, M, N up to IT8 and P to U up to IT7: ES = −ei + Δ, with Δ = ITn − IT(n−1) (ISO 286-1 special rule); above those grades, ES = −ei (K and N: ES = 0)
Maximum clearance = ES − ei; minimum clearance = EI − es; negative = interference; fit tolerance = IThole + ITshaft

Assumptions and limits

  • IT values (IT4 to IT11) and fundamental deviations for c, d, e, f, g, h, k, m, n, p, r, s, u from the ISO 286-1:2010 tables, by nominal size range (upper limit included). Reference temperature 20 °C / 68 °F (ISO 1).
  • Some letter and grade combinations follow the rule but are rare in practice; prefer the preferred fits of ISO 286-1 annex and ISO 1829. For inch drawings, ANSI B4.1 classes may be required by contract.

Standards and technical documents

  • ISO 286-1:2010: Geometrical product specifications (GPS) — ISO code system for tolerances on linear sizes — Part 1: Basis of tolerances, deviations and fits
  • ISO 286-2:2010: Part 2: Tables of standard tolerance classes and limit deviations for holes and shafts
  • ISO 1829: Selection of tolerance zones for general purposes
  • Machinery’s Handbook, 31st ed.: Preferred metric limits and fits

U.S. regulations

  • ASME B4.2: Preferred Metric Limits and Fits
  • ANSI B4.1: Preferred Limits and Fits for Cylindrical Parts (inch)
  • ASME Y14.5: Dimensioning and Tolerancing

Frequently asked questions

What is the H7 tolerance of a 2 in (50.8 mm) hole?

A 2.000 in bore falls in the 50 to 80 mm range, where IT7 is 30 µm (0.0012 in) and H has zero deviation: the bore runs from 2.0000 to 2.0012 in.

What is the difference between H7/g6 and H7/k6?

At Ø50 mm, H7/g6 gives 9 to 50 µm (0.0004 to 0.0020 in) clearance, so parts slide. H7/k6 is a transition fit, from 18 µm (0.0007 in) interference to 23 µm (0.0009 in) clearance, used for keyed pulleys and couplings.

What fit should I use for a bearing?

For a rotating inner ring under normal load, use k5 or k6 on the shaft up to about 100 mm (4 in) and m5 or m6 above. Housings are usually H7 or J7. Always check the bearing maker’s table.

How do I tell clearance from interference?

Take smallest hole minus largest shaft. If positive, there is always clearance. If largest hole minus smallest shaft is negative, there is always interference. In between, it is a transition fit.