H8/h8 fit — Locational clearance
H8/h8 is an ISO 286 hole-basis clearance fit. At Ø25 mm the hole is 25.000–25.033 mm and the shaft 24.967–25.000 mm, a clearance of 0.000–0.066 mm. Change the size below for other limits.
About H8/h8
General-purpose sliding and locating fit for parts that need to move freely but stay aligned.
At Ø25 mm the hole H8 measures 0 mm to +0.033 mm and the shaft h8 −0.033 mm to 0 mm, giving a clearance of 0.000 mm to 0.066 mm.
How the limits are calculated
Hole H8: fundamental deviation EI = 0, standard tolerance IT8 = 33 µm for 18–30 mm. Shaft h8: fundamental deviation es = 0, IT8 = 33 µm. Clearance = hole − shaft, evaluated at both extremes. See the fundamental deviation table for every letter. Values per ISO 286-1:2010.
H8/h8 limits by size range
| Size (mm) | Hole H8 | Shaft h8 | Clearance min | Clearance max |
|---|---|---|---|---|
| ≤ 3 | +0.014 / 0 | 0 / −0.014 | 0 | +0.028 |
| 3 – 6 | +0.018 / 0 | 0 / −0.018 | 0 | +0.036 |
| 6 – 10 | +0.022 / 0 | 0 / −0.022 | 0 | +0.044 |
| 10 – 18 | +0.027 / 0 | 0 / −0.027 | 0 | +0.054 |
| 18 – 30 | +0.033 / 0 | 0 / −0.033 | 0 | +0.066 |
| 30 – 50 | +0.039 / 0 | 0 / −0.039 | 0 | +0.078 |
| 50 – 80 | +0.046 / 0 | 0 / −0.046 | 0 | +0.092 |
| 80 – 120 | +0.054 / 0 | 0 / −0.054 | 0 | +0.108 |
| 120 – 180 | +0.063 / 0 | 0 / −0.063 | 0 | +0.126 |
| 180 – 250 | +0.072 / 0 | 0 / −0.072 | 0 | +0.144 |
| 250 – 315 | +0.081 / 0 | 0 / −0.081 | 0 | +0.162 |
| 315 – 400 | +0.089 / 0 | 0 / −0.089 | 0 | +0.178 |
| 400 – 500 | +0.097 / 0 | 0 / −0.097 | 0 | +0.194 |
Deviations in mm at the upper end of each range; negative clearance = interference. Clearance columns are shown on wider screens. Sub-ranges (e.g. 18–24 / 24–30) can differ for r, s, t, u, v, x, y, z — use the calculator for the exact size. “—” means ISO 286 doesn't define this class below that size (e.g. t only starts at 24 mm).
Is H8/h8 a clearance fit?
Yes — H8/h8 is a clearance fit per ISO 286 (see types of fits). At Ø25 mm it gives a clearance of 0.000 mm to 0.066 mm mm, depending which parts of the tolerance zones are paired.
What is the H8/h8 tolerance at 25 mm?
At a nominal size of Ø25 mm, H8 allows a hole diameter from 25.000 to 25.033 mm, and h8 allows a shaft diameter from 24.967 to 25.000 mm.
H8/h8 in practice
Where it's used
H8/h8 is a general-purpose locational clearance fit. Both zones touch the nominal size, so the minimum clearance is zero and the maximum is two IT8 bands. It suits parts that are slid on by hand and then fixed by a key, pin, set screw or shoulder: pulleys and collars on keyed shafts, hinge pins, guide sleeves, covers and spigots on general machinery. It is not a running fit: a pair at the tight end leaves no room for lubricant.
How to check it
Both GO gauges sit at the nominal size: the GO end of the plug gauge for the bore, and the GO ring or snap gauge for the shaft. That makes H8/h8 easy to check in the shop. For the first parts, record actual sizes: if both come out at their GO limits, the assembly is line-to-line and needs a push.
Easily confused with
H8/f7 looks similar on a drawing but is a running fit with guaranteed clearance. H7/h6 is the precision version of the same idea. H8/h7 sits between them: the bore stays H8 and the shaft is one grade finer.
Worked example
At Ø40 mm the H8 bore is 40.000–40.039 mm and the h8 shaft 39.961–40.000 mm. The clearance is 0.000–0.078 mm: zero at worst and under a tenth of a millimetre at best. That is enough to slide a pulley on by hand, but not enough for it to wobble once keyed.