This standard applies to features produced by machining, material removal, or similar processes. It covers four main types of geometric deviations: straightness, flatness, perpendicularity, and symmetry, as well as circular run-out and cylindrical run-out. By defining these defaults, the standard draws a line in the sand between what is critical to the function of the part and what is merely a consequence of the manufacturing process.
Furthermore, the standard is generally conservative. In high-precision industries such as aerospace or optical device manufacturing, even the "H" class may be too lenient for mating surfaces. Conversely, in heavy fabrication (like large structural steel), Class L might be too strict. Therefore, the standard is best utilized as a baseline for general machined parts, serving as a fallback rather than a substitute for thoughtful tolerance analysis. iso 2768 -2
ISO 2768-2 defines for geometrical characteristics (plus a “fine” class for runout only): This standard applies to features produced by machining,
| Characteristic | Tolerance (Class K) | |----------------|---------------------| | | 0.1 mm per 100 mm length | | Flatness | 0.2 mm per 100 mm × 100 mm | | Perpendicularity | 0.2 mm per 100 mm length | | Symmetry | 0.2 mm per feature length | | Circular runout | 0.1 mm (for class K) | Furthermore, the standard is generally conservative