Tolerance chart
h8 tolerance (shaft): ISO 286 chart up to 500 mm
h8 is an ISO tolerance class for shafts (external features) under ISO 286. At Ø25 mm it means 0 / −33 µm: the size may lie between 24.967 and 25.000 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 | 0 | −14 | 14 |
| 3 – 6 | 0 | −18 | 18 |
| 6 – 10 | 0 | −22 | 22 |
| 10 – 18 | 0 | −27 | 27 |
| 18 – 30 | 0 | −33 | 33 |
| 30 – 50 | 0 | −39 | 39 |
| 50 – 80 | 0 | −46 | 46 |
| 80 – 120 | 0 | −54 | 54 |
| 120 – 180 | 0 | −63 | 63 |
| 180 – 250 | 0 | −72 | 72 |
| 250 – 315 | 0 | −81 | 81 |
| 315 – 400 | 0 | −89 | 89 |
| 400 – 500 | 0 | −97 | 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 downwards: the shaft is never larger 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 24.967 and 25.000 mm.
Fits with h8 at Ø25 mm
Shaft-basis system: the shaft stays h8, the hole changes. Clearance in µm; a minus means interference. Sorted from the largest minimum clearance to the largest interference.
| Fit | Type | Max. clearance | Min. clearance |
|---|---|---|---|
| D9/h8 | clearance fit | 150 | 65 |
| E8/h8 | clearance fit | 106 | 40 |
| E9/h8 | clearance fit | 125 | 40 |
| F8/h8 | clearance fit | 86 | 20 |
| H8/h8 | clearance fit | 66 | 0 |
| H9/h8 | clearance fit | 85 | 0 |
Frequently asked questions about h8
What does h8 mean?
h8 is an ISO tolerance class for shafts (external features): the letter h sets the position of the tolerance zone, the number 8 the standard tolerance grade IT8. At Ø25 mm that gives 0 / −33 µm, i.e. 24.967 to 25.000 mm.
What are the h8 limits at Ø10 and Ø50 mm?
Ø10 h8: 0 / −22 µm (9.978 to 10.000 mm). Ø50 h8: 0 / −39 µm (49.961 to 50.000 mm).
Is h8 a clearance fit?
A tolerance class on its own is not a fit – only together with its mating part. H9/h8 at Ø25 mm is a clearance fit (maximum clearance 85 µm, minimum clearance 0 µm; a minus means interference).
More tolerance classes
Same letter h, other grades: h5 · h6 · h7 · h9 · h11
Shafts in grade 8: e8
All classes at a glance: ISO 286 tolerance charts. The same chart in German: h8 Toleranz.