ISO Tolerance Bands

The tolerance of size is normally defined as the difference between the upper and lower dimensions.

The need for tolerances to be identified on drawings is vital to allow assembly of parts in the desired way and interchangeability of parts as required in modern manufacturing methods.

ISO 286 implements 20 grades of accuracy to satisfy the requirements of different industries.

  • IT01,  IT0,   IT1,  IT2,   IT3,  IT4,  IT5,  IT6.. Production of gauges and instruments.
  • IT5,  IT6,  IT7,  IT8,  IT9,  IT10,  IT11,  IT12.. Precision and general Industry.
  • IT11,  IT14,   IT15,  IT16.. Semi finished products
  • IT16,  IT17,  IT18.. Structural Engineering
  • Examples in using above tables..

    Note: The tolerance band T is an absolute length value it does not have a negative value.

    Hole Dia 110mm H11,...

    Nearest zero ( El )= 110mm + 0mm = 110,000mm ..

    Furthest from zero ( ES )= 110mm + (0+ T=0,220)=110,220mm

    Resulting limits 110,000/110,220

    Shaft 110mm e9...
    Nearest zero ( es ) = 110mm - 0,072=109,928mm...

    Furthest from zero ( ei ) = 110mm - (0,072 + T=0,087) = 109,841mm

    Resulting limits 109,928/109,841

    Note for the tolerance bands which can be either side of zero, (J,K,N,j )

    The diagrams provided with the table clearly show calculation needed.e.g. consider Hole 300K7.

    T= 52 micrometres (0,052mm). Limit nearest zero ( K ) ES = 16 micrometres = (0,016mm)

    Limit furthest from zero ( K ) El = (0,016- 0,052)= -0,036

    Limits therefore (300 -0,036) = 299,964..and ...300+0,016= 300,016 limits 299,964/300,016 tolerance band in micrometres = (m-6) based on ISO 286  IT Grades 1 to 14  


    ISO Tolerance Band "T " 0 to 315mm

    Nominal Sizes (mm)
    over 1 3 6 10 18 30 50 80 120 180 250
    inc. 3 6 10 18 30 50 80 120 180 250 315
    IT Grade Tolerance Grade T
    1 0.8 1 1 1.2 1.5 1.5 2 2.5 3.5 4.5 6
    2 1.2 1.5 1.5 2 2.5 2.5 3 4 5 7 8
    3 2 2.5 2.5 3 4 4 5 6 8 10 12
    4 3 4 4 5 6 7 8 10 12 14 16
    5 4 5 6 8 9 11 13 15 18 20 23
    6 6 8 9 11 13 16 19 22 25 29 32
    7 10 12 15 18 21 25 30 35 40 46 52
    8 14 18 22 27 33 39 46 54 63 72 81
    9 25 30 36 43 52 62 74 87 100 115 130
    10 40 48 58 70 84 100 120 140 160 185 210
    11 60 75 90 110 130 160 190 220 250 290 320
    12 100 120 150 180 210 250 300 350 400 460 520
    13 140 180 220 270 330 390 460 540 630 720 810
    14 250 300 360 430 520 620 740 870 1000 1150 1300

    ISO Tolerance Band "T " 315 to 3150mm

    Nominal Size
    Over 250 315 400 500 630 800 1000 1250 1600 2000 2500
    Inclusive 315 400 500 630 800 1000 1250 1600 2000 2500 3150
    IT Grade Tolerance Grade T
    1 6 7 8 9 10 11 13 15 18 22 26
    2 8 9 10 11 13 15 18 21 25 30 36
    3 12 13 15 16 18 21 24 29 35 41 50
    4 16 18 20 22 25 28 33 39 46 55 68
    5 23 25 27 32 36 40 47 55 65 78 96
    6 32 36 40 44 50 56 66 78 92 110 135
    7 52 57 63 70 80 90 105 125 150 175 210
    8 81 89 97 110 125 140 165 195 230 280 330
    9 130 140 155 175 200 230 260 310 370 440 540
    10 210 230 250 280 320 360 420 500 600 700 860
    11 320 360 400 440 500 560 660 780 920 1100 1350
    12 520 570 630 700 800 900 1050 1250 1500 1750 2100
    13 810 890 970 1100 1250 1400 1650 1950 2300 2800 3300
    14 1300 1400 1550 1750 2000 2300 2600 3100 3700 4400 5400