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 require 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.
- IT 5, IT6, IT7, IT8, I9, IT10, IT11, IT12...Precision and general Industry.
- IT11, IT14, IT15, IT16..Semi finished products
- IT16, IT17, IT18 ..Structural Engineering
tolerance band in micrometres = (m-6)
based on ISO 286 IT Grades 1 to 14
| 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 | |||||||||||
| 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 |
