U8 tolerance (hole, IT8)

Hole tolerance class U8 per ISO 286-1:2010: fundamental deviation ES −18 … −540, grade IT8 (14 µm at ≤ 3 mm to 97 µm at 400–500 mm). For an exact size, open the calculator with U8 selected.

Type
Hole
Grade
IT8
Tolerance
14 … 97 µm
Fund. deviation
ES −18 … −540 µm

U8 limits by size range

Size (mm)Upper (µm)Lower (µm)Ø max (mm)Ø min (mm)
≤ 3−18−322.9822.968
3 – 6−23−415.9775.959
6 – 10−28−509.9729.950
10 – 14−33−6013.96713.940
14 – 18−33−6017.96717.940
18 – 24−41−7423.95923.926
24 – 30−48−8129.95229.919
30 – 40−60−9939.94039.901
40 – 50−70−10949.93049.891
50 – 65−87−13364.91364.867
65 – 80−102−14879.89879.852
80 – 100−124−17899.87699.822
100 – 120−144−198119.856119.802
120 – 140−170−233139.830139.767
140 – 160−190−253159.810159.747
160 – 180−210−273179.790179.727
180 – 200−236−308199.764199.692
200 – 225−258−330224.742224.670
225 – 250−284−356249.716249.644
250 – 280−315−396279.685279.604
280 – 315−350−431314.650314.569
315 – 355−390−479354.610354.521
355 – 400−435−524399.565399.476
400 – 450−490−587449.510449.413
450 – 500−540−637499.460499.363

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 U8

U8 denotes a hole tolerance zone with heavy interference deviation in the ISO 286 system.

At Ø25 mm U8 is −0.048 / −0.081 mm, i.e. 24.919 to 24.952 mm.

How the limits are calculated

U8 uses grade IT8 (a standard tolerance of 33 µm at 18–30 mm). Fundamental deviation: ES = −ei + Δ (Δ = ITn − IT(n−1), applied up to IT8 for K/M/N and IT7 otherwise); IT8 sets the width below ES. See the fundamental deviation table for every letter. Values per ISO 286-1:2010.

Related classes

U7