ISO 286 · clearance fit · IT8
h8 shaft tolerance
The h8 limits we cut to at every common nominal, computed from the ISO 286 fundamental deviation for h and the IT8 grade. Same numbers the configurator stamps on a h8 diameter.
h8 is a clearance class with its upper limit exactly at nominal: the shaft is never oversize, so a nominal-size bore always slides on. The letter h fixes where the band sits relative to nominal (the fundamental deviation); the grade 8 fixes how wide it is (IT8). Both come from the ISO 286 tables and scale with diameter, which is why one page per class, with every nominal, is more useful than a single number.
At a 1″ nominal the h8 band is +.0000 to -.0013: the shaft measures between 0.9987″ and 1″, a 0.0013″ window. The table gives the same limits at the inch and metric nominals we turn most.
Pick h8 on any diameter in the configurator and the drawing carries exactly these limits; the engine computes them from the standard for the diameter you enter, not from this table.
h8 limits by nominal diameter
| Nominal Ø | Upper dev. | Lower dev. | Max Ø (in) | Min Ø (in) | Band (in) |
|---|---|---|---|---|---|
| 1/4″ (0.25) | +.0000 | -.0009 | 0.25 | 0.2491 | 0.0009 |
| 3/8″ (0.375) | +.0000 | -.0009 | 0.375 | 0.3741 | 0.0009 |
| 1/2″ (0.5) | +.0000 | -.0011 | 0.5 | 0.4989 | 0.0011 |
| 5/8″ (0.625) | +.0000 | -.0011 | 0.625 | 0.6239 | 0.0011 |
| 3/4″ (0.75) | +.0000 | -.0013 | 0.75 | 0.7487 | 0.0013 |
| 7/8″ (0.875) | +.0000 | -.0013 | 0.875 | 0.8737 | 0.0013 |
| 1″ (1) | +.0000 | -.0013 | 1 | 0.9987 | 0.0013 |
| 1-1/8″ (1.125) | +.0000 | -.0013 | 1.125 | 1.1237 | 0.0013 |
| 1-1/4″ (1.25) | +.0000 | -.0015 | 1.25 | 1.2485 | 0.0015 |
| 1-3/8″ (1.375) | +.0000 | -.0015 | 1.375 | 1.3735 | 0.0015 |
| 1-1/2″ (1.5) | +.0000 | -.0015 | 1.5 | 1.4985 | 0.0015 |
| 1-3/4″ (1.75) | +.0000 | -.0015 | 1.75 | 1.7485 | 0.0015 |
| 2″ (2) | +.0000 | -.0018 | 2 | 1.9982 | 0.0018 |
| 2-1/2″ (2.5) | +.0000 | -.0018 | 2.5 | 2.4982 | 0.0018 |
| 3″ (3) | +.0000 | -.0018 | 3 | 2.9982 | 0.0018 |
| 4″ (4) | +.0000 | -.0021 | 4 | 3.9979 | 0.0021 |
| Metric nominals (limits in inches) | |||||
| 20 mm (0.7874″) | +.0000 | -.0013 | 0.7874 | 0.7861 | 0.0013 |
| 25 mm (0.9843″) | +.0000 | -.0013 | 0.9843 | 0.983 | 0.0013 |
| 30 mm (1.1811″) | +.0000 | -.0013 | 1.1811 | 1.1798 | 0.0013 |
| 35 mm (1.378″) | +.0000 | -.0015 | 1.378 | 1.3764 | 0.0015 |
| 40 mm (1.5748″) | +.0000 | -.0015 | 1.5748 | 1.5733 | 0.0015 |
| 45 mm (1.7717″) | +.0000 | -.0015 | 1.7717 | 1.7701 | 0.0015 |
| 50 mm (1.9685″) | +.0000 | -.0015 | 1.9685 | 1.967 | 0.0015 |
| 55 mm (2.1654″) | +.0000 | -.0018 | 2.1654 | 2.1635 | 0.0018 |
| 60 mm (2.3622″) | +.0000 | -.0018 | 2.3622 | 2.3604 | 0.0018 |
| 65 mm (2.5591″) | +.0000 | -.0018 | 2.5591 | 2.5572 | 0.0018 |
Deviations from nominal in inches at 0.0001 in resolution; max and min are the finished diameter limits. Metric nominals are converted and the limits shown in inches.
Applications and finish targets for h8
| Application | Finish target (Ra, µin) |
|---|---|
| Seal journal (rotary lip-seal running surface) | 16 |
Part of Shaft fits and tolerances. Other pages in the series: d9 · e8 · f7 · g6 · h6 · h7 · js6 · j6 · k5 · k6 · m6 · n6 · p6 · r6 · s6 · 1/4″ · 3/8″ · 1/2″ · 5/8″ · 3/4″ · 7/8″ · 1″ · 1-1/8″ · 1-1/4″ · 1-3/8″ · 1-1/2″ · 1-3/4″ · 2″ · 2-1/2″ · 3″ · 4″ · 20 mm · 25 mm · 30 mm · 35 mm · 40 mm · 45 mm · 50 mm · 55 mm · 60 mm · 65 mm.
Where h8 is used
These are the applications the configurator associates with h8, with the surface-finish target it applies to that diameter. A fit class sets size; the finish is what makes the size hold in service.
Clearance fit, by the numbers
Every h8 limit is at or below nominal, so against a nominal (H-basis) bore the minimum gap is 0″ and the maximum is set by the bore's own tolerance plus 0.0013″ at 1″. Tighter grades narrow the shaft's share of that range.
Frequently Asked Questions
These references are for specifying a part; every value here is one the configurator applies when you build one. Numbers are representative of the standard; check them against your part and its mating components before ordering. See all guides on the guides page.