ISO 286 · Fit Class Reference
ISO H7 tolerance chart
for bore dimensions
The H7 hole tolerance for every bore size from 0 to 500 mm - upper and lower limits at a glance. H means the hole is never under nominal; 7 sets how much over it may go.
| Nominal Ø (mm) | Lower limit | Upper limit | Tolerance |
|---|---|---|---|
| over 0 to 3 | +0.000 | +0.010 | 0.010 |
| over 3 to 6 | +0.000 | +0.012 | 0.012 |
| over 6 to 10 | +0.000 | +0.015 | 0.015 |
| over 10 to 18 | +0.000 | +0.018 | 0.018 |
| over 18 to 30 | +0.000 | +0.021 | 0.021 |
| over 30 to 50 | +0.000 | +0.025 | 0.025 |
| over 50 to 80 | +0.000 | +0.030 | 0.030 |
| over 80 to 120 | +0.000 | +0.035 | 0.035 |
| over 120 to 180 | +0.000 | +0.040 | 0.040 |
| over 180 to 250 | +0.000 | +0.046 | 0.046 |
| over 250 to 315 | +0.000 | +0.052 | 0.052 |
| over 315 to 400 | +0.000 | +0.057 | 0.057 |
| over 400 to 500 | +0.000 | +0.063 | 0.063 |
Lower deviation is 0 for every H hole · ranges are “over X up to and including Y” per ISO 286-1
How to read it
What H7 means, and why it is on so many drawings.
An ISO 286 fit code has two parts: a letter that fixes where the tolerance zone sits relative to the nominal size, and a number that sets how wide that zone is. For a hole, an uppercase H places the lower limit exactly at nominal - the hole is never smaller than the stated size. The 7 is the IT7 standard tolerance grade, which grows with the diameter, so a small bore gets a tight band and a large bore a wider one.
Why H7 is the default precision hole
H7 is the workhorse of hole-basis fits. Because the hole is fixed at H7, the fit is chosen by selecting the shaft: an H7/g6 gives a clearance fit that slides, H7/k6 a transition fit that locates, H7/p6 an interference fit that stays put. Holding the hole constant and varying the shaft is cheaper to manufacture, which is why H7 shows up on dowel holes, bearing bores, and locating features across nearly every precision drawing.
From the code to the Form 3
For inspection, a bare Ø30 H7 on a drawing has to become real limits - 30.000 to 30.021 - recorded as a characteristic. Done by hand, that means a chart like this one, a size lookup, and a transcription, for every fit-class callout on the part. Mavlon reads the fit class on the drawing and keeps it verbatim, and expands it to its actual limits when the numbers are needed - sourced, never on a guess. See how Mavlon interprets tolerances →
Stop looking it up by hand.
Mavlon reads H7 and every other fit class right off your drawing, into a Form 3 - limits expanded, source kept. Upload one free.