ISO 286 names a fit by pairing a hole tolerance with a
shaft tolerance, e.g. H7/g6. In this
hole-basis system the hole is kept constant — its letter is always
capital H, meaning its lower deviation is zero, so an H7
hole on a 25 mm nominal runs from 25.000 to 25.021 mm — and the
shaft is varied to set the fit. The opposite convention, a
shaft-basis system, fixes the shaft at letter h and
varies the hole; both reach the same fits, but hole-basis is preferred because a
reamer or plug gauge per hole is dearer than turning a shaft to size.
Read H7/g6 as: the part before the slash is the hole (capital letter
H, grade 7) and the part after is the shaft (lower-case
letter g, grade 6). The letter positions
the tolerance band relative to the nominal size — for clearance shafts (d, f, g, h)
it sits at or below nominal — and the number is the IT grade, which
sets how wide the band is. A negative clearance would mean
interference (the shaft is larger than the hole, an overlap that
must be pressed on); every fit in this table is a true clearance fit, so all the
clearance values are positive.
| Nominal size | Fit | Class | Hole dev. (µm) | Shaft dev. (µm) | Min clear. (µm) | Max clear. (µm) |
|---|---|---|---|---|---|---|
| 10 mm | H9/d9 (free running) | Clearance | 0 / +36 | −75 / −39 | 39 | 111 |
| 10 mm | H8/f7 (close running) | Clearance | 0 / +22 | −27 / −13 | 13 | 49 |
| 10 mm | H7/g6 (sliding) | Clearance | 0 / +14 | −14 / −5 | 5 | 28 |
| 10 mm | H7/h6 (locational clearance) | Clearance | 0 / +14 | −9 / 0 | 0 | 23 |
| 25 mm | H9/d9 (free running) | Clearance | 0 / +52 | −116 / −64 | 64 | 168 |
| 25 mm | H8/f7 (close running) | Clearance | 0 / +33 | −41 / −20 | 20 | 74 |
| 25 mm | H7/g6 (sliding) | Clearance | 0 / +21 | −20 / −7 | 7 | 41 |
| 25 mm | H7/h6 (locational clearance) | Clearance | 0 / +21 | −13 / 0 | 0 | 34 |
| 50 mm | H9/d9 (free running) | Clearance | 0 / +62 | −142 / −80 | 80 | 204 |
| 50 mm | H8/f7 (close running) | Clearance | 0 / +39 | −50 / −25 | 25 | 89 |
| 50 mm | H7/g6 (sliding) | Clearance | 0 / +25 | −25 / −9 | 9 | 50 |
| 50 mm | H7/h6 (locational clearance) | Clearance | 0 / +25 | −16 / 0 | 0 | 41 |
Source: ISO 286-1/-2 (computed by our ISO 286 calculator). Verify against the standard for your nominal size.
What is in (and out of) this table
These are hole-basis clearance fits — the shaft is always at or below the nominal size, so the assembly always has a gap. Listed loosest to tightest: H9/d9 (free running, generous clearance for speed or heat), H8/f7 (close running, rotates on an oil film), H7/g6 (sliding, locates closely yet slides by hand) and H7/h6 (locational clearance, just-touching with zero minimum clearance for easy assembly).
Transition fits (e.g. H7/k6, H7/n6) and interference / press fits (e.g. H7/p6, H7/s6) are not shown here: they involve a small or guaranteed overlap rather than a clearance, and our interference math lives in the press fit / interference calculator (contact pressure, assembly force, torque capacity and hub stress). For the clearance fits above, use the hole & shaft fit calculator to get the limits and clearance at any nominal size from 0–500 mm — it runs the exact function that generated this table, so the numbers will match.