Hole Tolerance & Fits Table (ISO 286)

ISO 286 is the standard code system for limits and fits on mating cylindrical parts. This page gives the ISO 286-1:2010 limit deviations for an H7 hole and the seven shaft classes most drawings use (f6, g6, h6, k6, n6, p6, s6) across the standard size bands up to 50mm, plus a fit-selection table mapping each common fit to its type, application, and assembly method. All values are in micrometres, taken from the standard’s own grade and fundamental-deviation tables.

How the ISO 286 fit system works

Every tolerance class has two parts: a letter that positions the tolerance zone and a number that sets its width. The letter is the fundamental deviation. Uppercase letters mark holes and lowercase letters mark shafts, so H7 is a hole and g6 is a shaft. The number is the IT grade, and ISO 286-1 fixes each grade’s width by nominal size: IT6 is 6µm wide up to 3mm and grows to 16µm at 30 to 50mm, while IT7 runs from 10µm to 25µm over the same range.

Reading a fit designation

A fit designation pairs a hole class with a shaft class, for example 25 H7/g6. The H hole zone always starts at nominal size: its lower deviation is 0 and its upper deviation equals the IT7 width. At 25mm that gives +21/0, so the hole measures 25.000 to 25.021mm. A g6 shaft at 25mm carries deviations of -7/-20, so it measures 24.980 to 24.993mm. To get the fit range, subtract the smallest shaft from the largest hole, and the largest shaft from the smallest hole: 7 to 41µm of clearance, always clearance and never interference.

Hole-basis versus shaft-basis

ISO 286-1 defines two fit systems. In a hole-basis system the hole is the basic feature: its lower limit equals nominal size, which is what the H classes give, and the fit character comes from the shaft class paired with it. In a shaft-basis system the shaft is basic: its upper limit equals nominal size, the h classes, and the hole class varies instead. Most general engineering work is hole-basis: holes come from standard drills and reamers, while shafts are turned to whatever the fit needs. Shaft-basis fits earn their keep when one fixed shaft, such as a ground bar or spindle, must carry several parts with different fit characters; the H7/k6 and K7/h6 rows below are the same fit built both ways.

Reading the deviation table

What the cells mean

Each cell lists the upper and lower limit deviations in micrometres relative to nominal size. The H7 hole spans 0 to +IT7. Shaft classes split into two patterns. For f, g, and h the fundamental deviation sits on top and the zone drops by the IT6 width: h6 starts at 0 and falls, g6 sits below h6 by 2 to 9µm depending on size, and f6 sits one step lower again. For k, n, p, and s the fundamental deviation sits on the bottom and the zone rises by the IT6 width, so k6 at 25mm is +15/+2.

Worked example: a 25mm bore

At 25mm, in the over-18-to-30 band, an H7 hole measures 25.000 to 25.021mm. Pair it with each shaft class:

• g6 (24.980 to 24.993mm): clearance 7 to 41µm, a sliding fit.
• h6 (24.987 to 25.000mm): clearance 0 to 34µm, a locating fit that can just reach zero clearance.
• k6 (25.002 to 25.015mm): up to 19µm of clearance or up to 15µm of interference, a transition fit.
• n6 (25.015 to 25.028mm): up to 6µm of clearance or up to 28µm of interference, a tight transition fit.
• p6 (25.022 to 25.035mm): interference 1 to 35µm, a press fit.
• s6 (25.035 to 25.048mm): interference 14 to 48µm, a medium drive fit.

Step to a 40mm bore, still in the over-30-to-50 band, and H7/p6 gives interference of 1 to 42µm: the minimum barely moves while the maximum grows with size. That pattern holds across the whole table, which is why a fit must always be checked in its own size band.

Choosing a fit class

Pick the fit character first (clearance, transition, or interference), then the tightest version your assembly tolerates. The table below maps the common H7 fits to their type, typical application, assembly method, and shaft-basis equivalent.

Three nuances worth checking

First, H7/n6 is a transition fit at these sizes, not a press fit: at 25mm the zones overlap by up to 6µm, so it suits parts that locate firmly yet still dismantle with light force. Second, H7/p6 only becomes a true interference fit from 3mm up. In the over-0-to-3 band the shaft minimum (+6µm) sits below the hole maximum (+10µm), so up to 4µm of clearance is possible; from 3 to 6mm the minimum interference is 0, with hole max equal to shaft min in the extreme case. Third, H7/u6 stays out of the deviation table because the u deviation splits twice (ei is +41, +48, +60, and +70µm across 18 to 24, 24 to 30, 30 to 40, and 40 to 50mm), so its values stay in the standard’s shaft table. For faster rotation, f6 is one step looser than g6: at 25mm H7/f6 runs 20 to 54µm of clearance, and wider pairs such as H8/f7, H9/d9, and H11/c11 trade precision for freedom under dirt, heat, and speed.

Limits of this table

The table covers nominal sizes up to 50mm and the classes most drawings call out. ISO 286-1 itself runs to 3150mm and grades IT01 to IT18, and ISO 286-2 republishes the deviations as ready-made limit tables. Limit deviations control size only: straightness, squareness, or position needs geometrical tolerances, either ISO 2768-2 general classes in the title block or ASME Y14.5 GD&T on the feature. A fit callout always overrides the drawing’s general-tolerance note. For interference fits, measure real parts before pressing: a 1µm minimum interference disappears quickly against measurement uncertainty or form error. Confirm values against the governing edition, ISO 286-1:2010 (confirmed 2026).