H9/f8 fit — Easy running fit
ISO 286 hole-basis clearance fit. Enter a nominal size to get the limits.
About H9/f8
Easy-running clearance for shafts in plain bearings where moderate speed and normal lubrication are expected but full IT7 precision isn't needed: fans, light gearboxes, farm-machinery drivetrains.
At Ø25 mm the hole H9 measures 0 mm to +0.052 mm and the shaft f8 −0.053 mm to −0.020 mm, giving a clearance of 0.020 mm to 0.105 mm.
How the limits are calculated
Hole H9: fundamental deviation EI = 0, standard tolerance IT9 = 52 µm for 18–30 mm. Shaft f8: fundamental deviation es = -20 µm, IT8 = 33 µm. Clearance = hole − shaft, evaluated at both extremes. See the fundamental deviation table for every letter. Values per ISO 286-1:2010.
H9/f8 limits by size range
| Size (mm) | Hole H9 | Shaft f8 | Clearance min | Clearance max |
|---|---|---|---|---|
| ≤ 3 | +0.025 / 0 | −0.006 / −0.020 | +0.006 | +0.045 |
| 3 – 6 | +0.030 / 0 | −0.010 / −0.028 | +0.010 | +0.058 |
| 6 – 10 | +0.036 / 0 | −0.013 / −0.035 | +0.013 | +0.071 |
| 10 – 18 | +0.043 / 0 | −0.016 / −0.043 | +0.016 | +0.086 |
| 18 – 30 | +0.052 / 0 | −0.020 / −0.053 | +0.020 | +0.105 |
| 30 – 50 | +0.062 / 0 | −0.025 / −0.064 | +0.025 | +0.126 |
| 50 – 80 | +0.074 / 0 | −0.030 / −0.076 | +0.030 | +0.150 |
| 80 – 120 | +0.087 / 0 | −0.036 / −0.090 | +0.036 | +0.177 |
| 120 – 180 | +0.100 / 0 | −0.043 / −0.106 | +0.043 | +0.206 |
| 180 – 250 | +0.115 / 0 | −0.050 / −0.122 | +0.050 | +0.237 |
| 250 – 315 | +0.130 / 0 | −0.056 / −0.137 | +0.056 | +0.267 |
| 315 – 400 | +0.140 / 0 | −0.062 / −0.151 | +0.062 | +0.291 |
| 400 – 500 | +0.155 / 0 | −0.068 / −0.165 | +0.068 | +0.320 |
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 H9/f8 a clearance fit?
Yes — H9/f8 is a clearance fit per ISO 286 (see types of fits). At Ø25 mm it gives a clearance of 0.020 mm to 0.105 mm mm, depending which parts of the tolerance zones are paired.
What is the H9/f8 tolerance at 25 mm?
At a nominal size of Ø25 mm, H9 allows a hole diameter from 25.000 to 25.052 mm, and f8 allows a shaft diameter from 24.947 to 24.980 mm.