Tolerances and standards
The tables list general tolerances for dimensions without individual specifications, achievable tolerances by process and ISO 286-1 IT grades in micrometres.
What a tolerance figure refers to
- Machine positioning accuracy
- Machine positioning accuracy is the machine builder's own figure for how precisely the axes arrive at a coordinate. It describes the machine rather than the part, and it does not belong on a drawing.
- Typical achievable tolerance
- Achievable part tolerance is what a finished feature is held to. It depends on the feature size, the material and the temperature it is measured at, so it is quoted per feature against the drawing.
- General tolerance standard
- The default drawing standard is what applies to every dimension the drawing leaves untoleranced. On machined and fabricated parts that is ISO 2768-mK, and the first table below writes it out. Moulded parts fall back to DIN 16742, which the achievable-tolerance table names per process.
ISO 2768-m general tolerance
±0.2 mm
CNC Machining, typical achievable
±0.005 mm
Both bands are drawn to scale from the figures in the tables below. A dimension the drawing leaves untoleranced takes the upper band. Machine positioning accuracy is not drawn, because no figure for it is published yet.
General tolerances, ISO 2768-mK
The m in ISO 2768-mK is the tolerance class for linear and angular dimensions. The K is the class for straightness, flatness, perpendicularity, symmetry and run out.
| Nominal size | Deviation |
|---|---|
| 0.5 to 3 | ±0.1 mm |
| over 3 to 6 | ±0.1 mm |
| over 6 to 30 | ±0.2 mm |
| over 30 to 120 | ±0.3 mm |
| over 120 to 400 | ±0.5 mm |
| over 400 to 1000 | ±0.8 mm |
| over 1000 to 2000 | ±1.2 mm |
| over 2000 to 4000 | ±2 mm |
| Nominal size | Deviation |
|---|---|
| 0.5 to 3 | ±0.2 mm |
| over 3 to 6 | ±0.5 mm |
| over 6 | ±1 mm |
| Shorter side | Deviation |
|---|---|
| up to 10 | ±1° |
| over 10 to 50 | ±0°30' |
| over 50 to 120 | ±0°20' |
| over 120 to 400 | ±0°10' |
| over 400 | ±0°5' |
| Nominal length | Tolerance |
|---|---|
| up to 10 | 0.05 mm |
| over 10 to 30 | 0.1 mm |
| over 30 to 100 | 0.2 mm |
| over 100 to 300 | 0.4 mm |
| over 300 to 1000 | 0.6 mm |
| over 1000 to 3000 | 0.8 mm |
| Shorter side | Tolerance |
|---|---|
| up to 100 | 0.4 mm |
| over 100 to 300 | 0.6 mm |
| over 300 to 1000 | 0.8 mm |
| over 1000 to 3000 | 1 mm |
| Nominal length | Tolerance |
|---|---|
| up to 100 | 0.6 mm |
| over 100 to 300 | 0.6 mm |
| over 300 to 1000 | 0.8 mm |
| over 1000 to 3000 | 1 mm |
Circular run out0.2 mm, at every nominal size
Tightest tolerance by process
| Process | Tightest tolerance on request |
|---|---|
| CNC Machining | On confirmation |
| CNC Turning | On confirmation |
| Sheet Metal Fabrication | On confirmation |
On confirmation means a figure is not published here until it has been confirmed in writing.
IT grades, IT6 to IT11
IT grades are the total tolerance band in micrometres, not a plus or minus figure. A size band runs above its lower figure and up to and including its upper one, so a 6 mm feature reads on 3–6 rather than on 6–10. IT6 is a ground or reamed fit. IT11 is the grade a saw cut or a drilled hole falls in.
| Nominal size | IT6 | IT7 | IT8 | IT9 | IT10 | IT11 |
|---|---|---|---|---|---|---|
| ≤3 | 6 µm | 10 µm | 14 µm | 25 µm | 40 µm | 60 µm |
| 3–6 | 8 µm | 12 µm | 18 µm | 30 µm | 48 µm | 75 µm |
| 6–10 | 9 µm | 15 µm | 22 µm | 36 µm | 58 µm | 90 µm |
| 10–18 | 11 µm | 18 µm | 27 µm | 43 µm | 70 µm | 110 µm |
| 18–30 | 13 µm | 21 µm | 33 µm | 52 µm | 84 µm | 130 µm |
| 30–50 | 16 µm | 25 µm | 39 µm | 62 µm | 100 µm | 160 µm |
| 50–80 | 19 µm | 30 µm | 46 µm | 74 µm | 120 µm | 190 µm |
| 80–120 | 22 µm | 35 µm | 54 µm | 87 µm | 140 µm | 220 µm |
| 120–180 | 25 µm | 40 µm | 63 µm | 100 µm | 160 µm | 250 µm |
| 180–250 | 29 µm | 46 µm | 72 µm | 115 µm | 185 µm | 290 µm |
| 250–315 | 32 µm | 52 µm | 81 µm | 130 µm | 210 µm | 320 µm |
| 315–400 | 36 µm | 57 µm | 89 µm | 140 µm | 230 µm | 360 µm |
| 400–500 | 40 µm | 63 µm | 97 µm | 155 µm | 250 µm | 400 µm |