f8 shaft tolerance (IT8)

Lower-case f8 is an ISO 286 shaft tolerance class (IT8, es −6 … −68 µm): at Ø10 mm the deviations are −0.013/−0.035 mm, at Ø25 mm −0.020/−0.053 mm (upper/lower). Looking for the F8 hole?

Shaft tolerance class f8 per ISO 286-1:2010: fundamental deviation es −6 … −68, grade IT8 (14 µm at ≤ 3 mm to 97 µm at 400–500 mm). For an exact size, open the calculator with f8 selected.

Type: Shaft
Grade: IT8
Tolerance: 14 … 97 µm
Fund. deviation: es −6 … −68 µm

f8 limits by size range

Size (mm)	Upper (µm)	Lower (µm)	Ø max (mm)	Ø min (mm)	Upper (mm)	Lower (mm)	Dev. (in)
≤ 3	−6	−20	2.994	2.980	−0.006	−0.020	−0.00024 / −0.00079
3 – 6	−10	−28	5.990	5.972	−0.010	−0.028	−0.00039 / −0.00110
6 – 10	−13	−35	9.987	9.965	−0.013	−0.035	−0.00051 / −0.00138
10 – 14	−16	−43	13.984	13.957	−0.016	−0.043	−0.00063 / −0.00169
14 – 18	−16	−43	17.984	17.957	−0.016	−0.043	−0.00063 / −0.00169
18 – 24	−20	−53	23.980	23.947	−0.020	−0.053	−0.00079 / −0.00209
24 – 30	−20	−53	29.980	29.947	−0.020	−0.053	−0.00079 / −0.00209
30 – 40	−25	−64	39.975	39.936	−0.025	−0.064	−0.00098 / −0.00252
40 – 50	−25	−64	49.975	49.936	−0.025	−0.064	−0.00098 / −0.00252
50 – 65	−30	−76	64.970	64.924	−0.030	−0.076	−0.00118 / −0.00299
65 – 80	−30	−76	79.970	79.924	−0.030	−0.076	−0.00118 / −0.00299
80 – 100	−36	−90	99.964	99.910	−0.036	−0.090	−0.00142 / −0.00354
100 – 120	−36	−90	119.964	119.910	−0.036	−0.090	−0.00142 / −0.00354
120 – 140	−43	−106	139.957	139.894	−0.043	−0.106	−0.00169 / −0.00417
140 – 160	−43	−106	159.957	159.894	−0.043	−0.106	−0.00169 / −0.00417
160 – 180	−43	−106	179.957	179.894	−0.043	−0.106	−0.00169 / −0.00417
180 – 200	−50	−122	199.950	199.878	−0.050	−0.122	−0.00197 / −0.00480
200 – 225	−50	−122	224.950	224.878	−0.050	−0.122	−0.00197 / −0.00480
225 – 250	−50	−122	249.950	249.878	−0.050	−0.122	−0.00197 / −0.00480
250 – 280	−56	−137	279.944	279.863	−0.056	−0.137	−0.00220 / −0.00539
280 – 315	−56	−137	314.944	314.863	−0.056	−0.137	−0.00220 / −0.00539
315 – 355	−62	−151	354.938	354.849	−0.062	−0.151	−0.00244 / −0.00594
355 – 400	−62	−151	399.938	399.849	−0.062	−0.151	−0.00244 / −0.00594
400 – 450	−68	−165	449.932	449.835	−0.068	−0.165	−0.00268 / −0.00650
450 – 500	−68	−165	499.932	499.835	−0.068	−0.165	−0.00268 / −0.00650

Deviations at the upper end of each range (Ø columns use that size); use the calculator for the exact size. — : not defined by ISO 286 for that size. Upper/Lower (mm) and inch columns are shown on wider screens.

About f8

f8 denotes a shaft tolerance zone with close running deviation in the ISO 286 system. It is used in 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 f8 is −0.020 / −0.053 mm, i.e. 24.947 to 24.980 mm.

How the limits are calculated

f8 uses grade IT8 (a standard tolerance of 33 µm at 18–30 mm). Fundamental deviation: es is tabulated directly by ISO 286-1 Table 2; ei = es − IT8. See the fundamental deviation table for every letter. Values per ISO 286-1:2010.

f8 in practice

Where it's used

f8 is a running-fit shaft with a guaranteed gap below the nominal size. f8 journals turn in H8 or H9 bores (H9/f8 is in the preferred list) in fans, light gearboxes, conveyors and farm-machinery drivetrains, where grease or oil needs room and the shaft is turned rather than ground. The f deviation is small, so the fit still locates reasonably well while running freely.

How to check it

Use an outside micrometer or a snap gauge. For a shaft the gauge logic is the reverse of a bore: the GO side of the snap gauge is set to the upper limit (the largest acceptable shaft), the NO-GO side to the lower limit. Measure in two directions 90° apart and at both ends of the journal to catch ovality and taper from turning.

Easily confused with

F8 in capitals is a hole class, with its zone above the nominal size. f7 is the usual partner of H8 in close running fits; f8 trades a little precision for a cheaper shaft. And f is not a typo for h: an f shaft is deliberately undersize, so a journal drawn as Ø25 f8 is never exactly 25 mm.

Worked example

At Ø25 mm, f8 is −0.020/−0.053 mm, so the shaft measures 24.947–24.980 mm. In an H9 bore that gives 0.020–0.105 mm of clearance; in a tighter H8 bore, 0.020–0.086 mm.

Fits using f8

H9/f8 All fits →