IT Grade
IT grade(s) refer to an internationally accepted code system for tolerances on linear dimensions. Such code systems may be used to produce interchangeable parts. In engineering, the word tolerance refers to a range of allowable dimensions or values. Standard tolerance grades are a group of tolerances for linear sizes characterized by a common identifier. For SI measurements, a system of tolerance grades defined in ISO 286 is frequently used and identified by the letters IT followed by a number specifying how precise the requirements are, relative to the nominal size of a part.
For example, IT14 refers to a group of tolerances used in manufacturing. For a part dimensioned at 10 mm, IT14 allows for up to 0.36 mm of variation in size. As the IT grade number increases, the tolerances increase; similarly, for larger nominal sizes, the standard tolerances increase. For a part dimensioned at 100 mm, IT14 allows for up to 0.87 mm of variation in size.
The ISO 286 defines the international tolerances grades for nominal sizes up to 3.15 meters as follows:[1]
Nominal size | International tolerance grade | ||||||||||||||||||||||||||||||||||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
> | ≤ | IT01 | IT0 | IT1 | IT2 | IT3 | IT4 | IT5 | IT6 | IT7 | IT8 | IT9 | IT10 | IT11 | IT12 | IT13 | IT14 | IT15 | IT16 | IT17 | IT18 | ||||||||||||||||||||||
mm | tolerance in µm | tolerance in mm | |||||||||||||||||||||||||||||||||||||||||
0 | 3 | 0 |
.3 | 0 |
.5 | 0 |
.8 | 1 |
.2 | 2 |
.0 | 1 | 1 | 6 | 10 | 14 | 25 | 40 | 60 | 0 |
.10 | 0 |
.14 | 0 |
.25 | 0 |
.40 | 0 |
.60 | 1 |
.00 | 1.40 | |||||||||||
3 | 6 | 0 |
.4 | 0 |
.6 | 1 |
.0 | 1 |
.5 | 2 |
.5 | 1 | 5 | 8 | 12 | 18 | 30 | 48 | 75 | 0 |
.12 | 0 |
.18 | 0 |
.30 | 0 |
.48 | 0 |
.75 | 1 |
.20 | 1.80 | |||||||||||
6 | 10 | 0 |
.4 | 0 |
.6 | 1 |
.0 | 1 |
.5 | 2 |
.5 | 4 | 6 | 9 | 15 | 22 | 36 | 58 | 90 | 0 |
.15 | 0 |
.22 | 0 |
.36 | 0 |
.58 | 0 |
.90 | 1 |
.50 | 2.20 | |||||||||||
10 | 18 | 0 |
.5 | 0 |
.8 | 1 |
.2 | 2 |
.0 | 3 | 5 | 8 | 11 | 18 | 27 | 43 | 70 | 110 | 0 |
.18 | 0 |
.27 | 0 |
.43 | 0 |
.70 | 1 |
.10 | 1 |
.80 | 2.70 | ||||||||||||
18 | 30 | 0 |
.6 | 1 |
.0 | 1 |
.5 | 2 |
.5 | 4 | 6 | 9 | 13 | 21 | 33 | 52 | 84 | 130 | 0 |
.21 | 0 |
.33 | 0 |
.52 | 0 |
.84 | 1 |
.30 | 2 |
.10 | 3.30 | ||||||||||||
30 | 50 | 0 |
.6 | 1 |
.0 | 1 |
.5 | 2 |
.5 | 4 | 7 | 11 | 16 | 25 | 39 | 62 | 100 | 160 | 0 |
.25 | 0 |
.39 | 0 |
.62 | 1 |
.00 | 1 |
.60 | 2 |
.50 | 3.90 | ||||||||||||
50 | 80 | 0 |
.8 | 1 |
.2 | 2 |
.0 | 3 | 5 | 8 | 13 | 19 | 30 | 46 | 74 | 120 | 190 | 0 |
.30 | 0 |
.46 | 0 |
.74 | 1 |
.20 | 1 |
.90 | 3 |
.00 | 4.60 | |||||||||||||
80 | 120 | 1 |
.0 | 1 |
.5 | 2 |
.5 | 4 | 6 | 10 | 15 | 22 | 35 | 54 | 87 | 140 | 220 | 0 |
.35 | 0 |
.54 | 0 |
.87 | 1 |
.40 | 2 |
.20 | 3 |
.50 | 5.40 | |||||||||||||
120 | 180 | 1 |
.2 | 2 | 3 |
.5 | 5 | 8 | 12 | 18 | 25 | 40 | 63 | 100 | 160 | 250 | 0 |
.40 | 0 |
.63 | 1 |
.00 | 1 |
.60 | 2 |
.50 | 4 |
.00 | 6.30 | ||||||||||||||
180 | 250 | 2 |
.0 | 3 | 4 |
.5 | 7 | 10 | 14 | 20 | 29 | 46 | 72 | 115 | 185 | 290 | 0 |
.46 | 0 |
.72 | 1 |
.15 | 1 |
.85 | 2 |
.90 | 4 |
.60 | 7.20 | ||||||||||||||
250 | 315 | 2 |
.5 | 4 | 6 | 8 | 12 | 16 | 23 | 32 | 52 | 81 | 130 | 210 | 320 | 0 |
.52 | 0 |
.81 | 1 |
.30 | 2 |
.10 | 3 |
.20 | 5 |
.20 | 8.10 | |||||||||||||||
315 | 400 | 3 | 5 | 7 | 9 | 13 | 18 | 25 | 36 | 57 | 89 | 140 | 230 | 360 | 0 |
.57 | 0 |
.89 | 1 |
.40 | 2 |
.30 | 3 |
.60 | 5 |
.70 | 8.90 | ||||||||||||||||
400 | 500 | 4 | 6 | 8 | 10 | 15 | 20 | 27 | 40 | 63 | 97 | 155 | 250 | 400 | 0 |
.63 | 0 |
.97 | 1 |
.55 | 2 |
.50 | 4 |
.00 | 6 |
.30 | 9.70 | ||||||||||||||||
500 | 630 | 9 | 11 | 16 | 22 | 32 | 44 | 70 | 110 | 175 | 280 | 440 | 0 |
.70 | 1 |
.10 | 1 |
.75 | 2 |
.80 | 4 |
.40 | 7 |
.00 | 11.00 | ||||||||||||||||||
630 | 800 | 10 | 13 | 18 | 25 | 36 | 50 | 80 | 125 | 200 | 320 | 500 | 0 |
.80 | 1 |
.25 | 2 |
.00 | 3 |
.20 | 5 |
.00 | 8 |
.00 | 12.50 | ||||||||||||||||||
800 | 1,000 | 11 | 15 | 21 | 28 | 40 | 56 | 90 | 140 | 230 | 360 | 560 | 0 |
.90 | 1 |
.40 | 2 |
.30 | 3 |
.60 | 5 |
.60 | 9 |
.00 | 14.00 | ||||||||||||||||||
1,000 | 1,250 | 13 | 18 | 24 | 33 | 47 | 66 | 105 | 165 | 260 | 420 | 660 | 1 |
.05 | 1 |
.65 | 2 |
.60 | 4 |
.20 | 6 |
.60 | 10 |
.50 | 16.50 | ||||||||||||||||||
1,250 | 1,600 | 15 | 21 | 29 | 39 | 55 | 78 | 125 | 195 | 310 | 500 | 780 | 1 |
.25 | 1 |
.95 | 3 |
.10 | 5 |
.00 | 7 |
.80 | 12 |
.50 | 19.50 | ||||||||||||||||||
1,600 | 2,000 | 18 | 25 | 35 | 46 | 65 | 92 | 150 | 230 | 370 | 600 | 920 | 1 |
.50 | 2 |
.30 | 3 |
.70 | 6 |
.00 | 9 |
.20 | 15 |
.00 | 23.00 | ||||||||||||||||||
2,000 | 2,500 | 22 | 30 | 41 | 55 | 78 | 110 | 175 | 280 | 440 | 700 | 1,100 | 1 |
.75 | 2 |
.80 | 4 |
.40 | 7 |
.00 | 11 |
.00 | 17 |
.50 | 28.00 | ||||||||||||||||||
2,500 | 3,150 | 26 | 36 | 50 | 68 | 96 | 135 | 210 | 330 | 540 | 860 | 1,350 | 2 |
.10 | 3 |
.30 | 5 |
.40 | 8 |
.60 | 13 |
.50 | 21 |
.00 | 33.00 |
From IT6 to IT18, the standard tolerances are multiplied by the factor 10 at each fifth step. This rule applies to all standard tolerances and may be used to extrapolate values for IT grades not given in Table 1. For example, the nominal size range 120 mm up to and including 180 mm, the value of IT20 is:
IT20 = IT15 × 10 = 1.6 mm × 10 = 16 mm [2]
An industrial process may have an IT grade associated with it, indicating how precise it is. When designing a part, an engineer will typically determine a critical dimension (D) and some tolerance (T) on that dimension. Using this formula, the engineer can determine what IT Grade is necessary to produce the part with those specifications. Thus, if injection molding has is IT13 and apart requires IT5, one cannot use injection molding to produce that part to those specifications. It is useful in determining the processes capable of producing parts to a specification.
See also
References
- ^ International Organization for Standardization. ISO 286-1:2010 Gemoetrical product specification (GPS) - ISO code system for tolerences on linear sizes, Part 1. p. 20.
- ^ Ibid. p. 12
External links
- ISO Hole and Shaft tolerances/limits, Roymech, UK.
- ISO Hole and Shaft Tolerances iPhone App, Trelleborg Sealing Solutions Germany.