Tolerance chart
H8 tolerance (hole): ISO 286 chart up to 500 mm
H8 is an ISO tolerance class for holes (internal features) under ISO 286. At Ø25 mm it means +33 / 0 µm: the size may lie between 25.000 and 25.033 mm. Below are the deviations for every nominal size up to 500 mm and the fits that use H8.
H8 chart: deviations for all nominal sizes up to 500 mm
Deviations in µm (1 µm = 0.001 mm). A nominal size belongs to the row »over … up to and including …«: exactly 30 mm is in the row ending at 30, 30.1 mm in the next one.
| Nominal size over – to (mm) | Upper deviation | Lower deviation | Tolerance |
|---|---|---|---|
| 0 – 3 | +14 | 0 | 14 |
| 3 – 6 | +18 | 0 | 18 |
| 6 – 10 | +22 | 0 | 22 |
| 10 – 18 | +27 | 0 | 27 |
| 18 – 30 | +33 | 0 | 33 |
| 30 – 50 | +39 | 0 | 39 |
| 50 – 80 | +46 | 0 | 46 |
| 80 – 120 | +54 | 0 | 54 |
| 120 – 180 | +63 | 0 | 63 |
| 180 – 250 | +72 | 0 | 72 |
| 250 – 315 | +81 | 0 | 81 |
| 315 – 400 | +89 | 0 | 89 |
| 400 – 500 | +97 | 0 | 97 |
H8 for your nominal size
How H8 is built
An ISO tolerance class is a letter and a number. Capital letters stand for holes, small letters for shafts. The letter H sets the position of the tolerance zone; at Ø25 mm it lies from the nominal size upwards: the hole is never smaller than nominal. The number 8 is the standard tolerance grade IT8: it sets how wide the zone is – 33 µm at Ø25 mm.
The tolerance grows with the nominal size: 14 µm in the smallest row (0 – 3 mm), 97 µm in the largest (400 – 500 mm). On a drawing the class follows the dimension, as in »Ø25 H8«; the inspection plan turns that into the limits 25.000 and 25.033 mm.
Fits with H8 at Ø25 mm
Hole-basis system: the hole stays H8, the shaft changes. Clearance in µm; a minus means interference. Sorted from the largest minimum clearance to the largest interference.
| Fit | Type | Max. clearance | Min. clearance |
|---|---|---|---|
| H8/e7 | clearance fit | 94 | 40 |
| H8/e8 | clearance fit | 106 | 40 |
| H8/f7 | clearance fit | 74 | 20 |
| H8/h7 | clearance fit | 54 | 0 |
| H8/h8 | clearance fit | 66 | 0 |
Frequently asked questions about H8
What does H8 mean?
H8 is an ISO tolerance class for holes (internal features): the letter H sets the position of the tolerance zone, the number 8 the standard tolerance grade IT8. At Ø25 mm that gives +33 / 0 µm, i.e. 25.000 to 25.033 mm.
What are the H8 limits at Ø10 and Ø50 mm?
Ø10 H8: +22 / 0 µm (10.000 to 10.022 mm). Ø50 H8: +39 / 0 µm (50.000 to 50.039 mm).
Is H8 a clearance fit?
A tolerance class on its own is not a fit – only together with its mating part. H8/e7 at Ø25 mm is a clearance fit (maximum clearance 94 µm, minimum clearance 40 µm; a minus means interference).
More tolerance classes
Same letter H, other grades: H6 · H7 · H9 · H10 · H11
All classes at a glance: ISO 286 tolerance charts. The same chart in German: H8 Toleranz.