H7/f7 fit — Close running fit
H7/f7 is an ISO 286 hole-basis clearance fit. At Ø25 mm the hole is 25.000–25.021 mm and the shaft 24.959–24.980 mm, a clearance of 0.020–0.062 mm. Change the size below for other limits.
About H7/f7
Sliding parts and journals at moderate speeds with noticeable but small play.
At Ø25 mm the hole H7 measures 0 mm to +0.021 mm and the shaft f7 −0.041 mm to −0.020 mm, giving a clearance of 0.020 mm to 0.062 mm.
How the limits are calculated
Hole H7: fundamental deviation EI = 0, standard tolerance IT7 = 21 µm for 18–30 mm. Shaft f7: fundamental deviation es = -20 µm, IT7 = 21 µm. Clearance = hole − shaft, evaluated at both extremes. See the fundamental deviation table for every letter. Values per ISO 286-1:2010.
H7/f7 limits by size range
| Size (mm) | Hole H7 | Shaft f7 | Clearance min | Clearance max |
|---|---|---|---|---|
| ≤ 3 | +0.010 / 0 | −0.006 / −0.016 | +0.006 | +0.026 |
| 3 – 6 | +0.012 / 0 | −0.010 / −0.022 | +0.010 | +0.034 |
| 6 – 10 | +0.015 / 0 | −0.013 / −0.028 | +0.013 | +0.043 |
| 10 – 18 | +0.018 / 0 | −0.016 / −0.034 | +0.016 | +0.052 |
| 18 – 30 | +0.021 / 0 | −0.020 / −0.041 | +0.020 | +0.062 |
| 30 – 50 | +0.025 / 0 | −0.025 / −0.050 | +0.025 | +0.075 |
| 50 – 80 | +0.030 / 0 | −0.030 / −0.060 | +0.030 | +0.090 |
| 80 – 120 | +0.035 / 0 | −0.036 / −0.071 | +0.036 | +0.106 |
| 120 – 180 | +0.040 / 0 | −0.043 / −0.083 | +0.043 | +0.123 |
| 180 – 250 | +0.046 / 0 | −0.050 / −0.096 | +0.050 | +0.142 |
| 250 – 315 | +0.052 / 0 | −0.056 / −0.108 | +0.056 | +0.160 |
| 315 – 400 | +0.057 / 0 | −0.062 / −0.119 | +0.062 | +0.176 |
| 400 – 500 | +0.063 / 0 | −0.068 / −0.131 | +0.068 | +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 H7/f7 a clearance fit?
Yes — H7/f7 is a clearance fit per ISO 286 (see types of fits). At Ø25 mm it gives a clearance of 0.020 mm to 0.062 mm mm, depending which parts of the tolerance zones are paired.
What is the H7/f7 tolerance at 25 mm?
At a nominal size of Ø25 mm, H7 allows a hole diameter from 25.000 to 25.021 mm, and f7 allows a shaft diameter from 24.959 to 24.980 mm.
H7/f7 in practice
Where it's used
H7/f7 is a close running fit with a small, guaranteed clearance: journals in bronze or sintered bushes at moderate speed, gearbox and pump shafts in plain bearings, and sliding parts that need noticeable but small play. Compared with the ISO preferred close running fit H8/f7, it tightens the bore by one grade, which narrows the spread of clearance from one pair of parts to the next.
How to check it
Gauge the bore (GO at the nominal size, NO-GO at the upper limit) and the shaft (GO at the upper limit of f7, NO-GO at the lower) separately. Don't approve the fit by feel: a pair that turns smoothly in the workshop may be at the tight end of the band and seize once the shaft warms faster than the housing. If the bush is pressed in, measure the bore after pressing, because it closes up.
Easily confused with
H7/g6 is a sliding fit with much less clearance. H8/f7 is the ISO preferred close running fit, with a coarser bore. F7/h6 is the shaft-basis counterpart with the same intent, but the deviations sit on the hole, so the clearances are not identical.
Worked example
A Ø30 shaft in a pressed-in bush: H7 bore 30.000–30.021 mm, f7 shaft 29.959–29.980 mm, diametral clearance 0.020–0.062 mm. The usual rule of thumb for oil-lubricated journals, about 1 µm of clearance per millimetre of diameter, sits inside that band.