Used for precision components requiring high accuracy.
Angular deviations are measured across the longest side of the angle and are expressed in millimeters per meter (mm/m):
The story within the PDF revealed a legendary project from the late 80s: The Phoenix Probe. The engineers had simplified their drawings by using ISO 2768-m for linear dimensions, assuming the medium class would be enough. But they forgot Part 2—the geometrical tolerances for things like straightness and symmetry.
High-quality reference PDFs often include quick visual diagrams that demonstrate exactly how to measure "the shorter leg of an angle" or define "broken edges," eliminating ambiguity during quality assurance checks. Best Practices for Using the Standard iso 2768 general tolerances pdf exclusive
ISO 2768 groups tolerances by:
The ISO 2768 standard defines two types of tolerances:
The magic of ISO 2768-1 lies in its four tolerance classes, which range from high precision to very loose manufacturing allowances. These classes are designated by single letters: Used for precision components requiring high accuracy
Together, ISO 2768-1 and ISO 2768-2 superseded the original ISO 2768:1973. These standards are also adopted regionally — for instance, as in Germany and BS EN 22768 in the United Kingdom.
The standard is divided into two distinct parts that work together to define a part's precision level: Part Focus Area Tolerance Classes Key Controlled Features Linear & Angular f (fine), m (medium), c (coarse), v (very coarse) Lengths, diameters, radii, chamfer heights, angles. Part 2 Geometrical
While it is tempting to choose ISO 2768-fH to ensure perfect parts, tighter tolerances require slower manufacturing speeds, specialized tooling, and higher scrap rates. Stick to mk unless design constraints demand otherwise. But they forgot Part 2—the geometrical tolerances for
ISO 2768-2 establishes three tolerance classes: , K , and L . Straightness and Flatness
— Remember: Part 1 uses lowercase letters (f, m, c, v), while Part 2 uses uppercase letters (H, K, L). A drawing marked "ISO 2768-mK" is correct; "ISO 2768-MK" would be incorrect.
Tolerances are selected based on the length of the largest surface or line.