General Tolerances for Symmetry
Symmetry is included in the general tolerances of the ISO 2768-2:1989 standard. It defines how precisely the centerline or center plane of a part is positioned in relation to opposing surfaces or structures when a separate tolerance is not specified.
General tolerances ensure that asymmetry remains within controlled limits and that parts function as intended, for example in rotating components, joints, and aesthetically visible structures. At the same time, they prevent unnecessarily tight tolerances from being specified, which eases manufacturing and reduces costs.
As with other general tolerances, there's no need to mark symmetry separately on the drawing—an indication like ISO 2768-mK is sufficient. This shows that permissible deviations according to the standard also apply to symmetry.
General Tolerance Table for Symmetry
| Tolerance Class | Straightness and Flatness Tolerances by Nominal Length Range | ||||
| Designation | > | 100 | 300 | 1000 | |
| ≤ | 100 | 300 | 1000 | 3000 | |
| H | 0.5 | 0.5 | 0.5 | 0.5 | |
| K | 0.6 | 0.6 | 0.8 | 1 | |
| L | 0.6 | 1 | 1.5 | 2 | |
The values in the table are given in millimeters (mm).
