h12 shaft tolerance (IT12)

Lower-case h12 is an ISO 286 shaft tolerance class (IT12, es = 0): at Ø10 mm the deviations are 0/−0.150 mm, at Ø25 mm 0/−0.210 mm (upper/lower). Looking for the H12 hole?

Shaft tolerance class h12 per ISO 286-1:2010: fundamental deviation es = 0, grade IT12 (100 µm at ≤ 3 mm to 630 µm at 400–500 mm). For an exact size, open the calculator with h12 selected.

Type: Shaft
Grade: IT12
Tolerance: 100 … 630 µm
Fund. deviation: es = 0

h12 limits by size range

Size (mm)	Lower (µm)	Ø max (mm)	Ø min (mm)	Lower (mm)	Dev. (in)
≤ 3	−100	3.000	2.900	−0.100	0 / −0.00394
3 – 6	−120	6.000	5.880	−0.120	0 / −0.00472
6 – 10	−150	10.000	9.850	−0.150	0 / −0.00591
10 – 14	−180	14.000	13.820	−0.180	0 / −0.00709
14 – 18	−180	18.000	17.820	−0.180	0 / −0.00709
18 – 24	−210	24.000	23.790	−0.210	0 / −0.00827
24 – 30	−210	30.000	29.790	−0.210	0 / −0.00827
30 – 40	−250	40.000	39.750	−0.250	0 / −0.00984
40 – 50	−250	50.000	49.750	−0.250	0 / −0.00984
50 – 65	−300	65.000	64.700	−0.300	0 / −0.01181
65 – 80	−300	80.000	79.700	−0.300	0 / −0.01181
80 – 100	−350	100.000	99.650	−0.350	0 / −0.01378
100 – 120	−350	120.000	119.650	−0.350	0 / −0.01378
120 – 140	−400	140.000	139.600	−0.400	0 / −0.01575
140 – 160	−400	160.000	159.600	−0.400	0 / −0.01575
160 – 180	−400	180.000	179.600	−0.400	0 / −0.01575
180 – 200	−460	200.000	199.540	−0.460	0 / −0.01811
200 – 225	−460	225.000	224.540	−0.460	0 / −0.01811
225 – 250	−460	250.000	249.540	−0.460	0 / −0.01811
250 – 280	−520	280.000	279.480	−0.520	0 / −0.02047
280 – 315	−520	315.000	314.480	−0.520	0 / −0.02047
315 – 355	−570	355.000	354.430	−0.570	0 / −0.02244
355 – 400	−570	400.000	399.430	−0.570	0 / −0.02244
400 – 450	−630	450.000	449.370	−0.630	0 / −0.02480
450 – 500	−630	500.000	499.370	−0.630	0 / −0.02480

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 h12

h12 denotes a shaft tolerance zone with zero line deviation in the ISO 286 system.

At Ø25 mm h12 is 0 / −0.210 mm, i.e. 24.790 to 25.000 mm.

How the limits are calculated

h12 uses grade IT12 (a standard tolerance of 210 µm at 18–30 mm). Fundamental deviation: es = 0: the tolerance zone sits entirely below the nominal size, and IT12 sets its width. See the fundamental deviation table for every letter. Values per ISO 286-1:2010.

h12 in practice

Where it's used

h12 is a coarse shaft class for diameters that form no running or locating fit: collars, the outside of spacers, handles and knobs, parts that sit in a generous clearance hole, and turned features where only 'not too big' matters. With es = 0 the part never exceeds the nominal size, so it always enters an H hole of the same nominal size.

How to check it

A digital caliper is the normal check. IT12 runs from 0.1 mm at the smallest sizes to over half a millimetre at 500 mm, well clear of the caliper's resolution. For batches, a snap gauge with GO at the nominal size and NO-GO at the lower limit is faster. Measure across the full diameter, not on a burr or the edge of a chamfer.

Easily confused with

H12 in capitals is the hole class. h12 is also often mixed up with a general tolerance. ISO 2768-m is symmetric (±) and wider overall at every size, whereas h12 is one-sided and entirely below the nominal size. If the title block says ISO 2768-m and the feature says h12, h12 governs that feature.

Worked example

The outside of a Ø30 spacer in h12 measures 29.790–30.000 mm (0/−0.210 mm). In a Ø30 H11 bore (30.000–30.130 mm) it always goes in: the clearance is 0.000–0.340 mm.