While there are other classes—such as "f" (fine) for high precision or "c" (coarse) for loose fits—the combination is the most widely used, representing about 80% of typical manufacturing requirements.
ISO standards are continuously reviewed and updated to meet the evolving needs of global industry. While the 1989 version remains widely accepted, a new revised version, ISO 2768:2026, is currently in development and will likely introduce clarifications and modernizations to the standard. Engineers and manufacturers should stay informed about these upcoming changes to ensure their practices remain compliant with the latest international guidelines.
These control the acceptable variance in angular degrees based on the length of the shorter leg of the angle. Length of Shorter Leg (mm) Tolerance Deviation for Class "m" ±plus or minus 1∘1 raised to the composed with power Over 10 to 50 ±plus or minus Over 50 to 120 ±plus or minus Over 120 to 400 ±plus or minus ±plus or minus ISO 2768-2: The "k" Class (Geometrical Tolerances)
Therefore, indicates that a component must meet Medium linear tolerances and Medium geometrical tolerances . ISO 2768-m Linear Tolerances (Part 1) general tolerance iso 2768-mk
This section covers geometric deviations (form and position) for features without individual tolerance indications. It is divided into three classes:
Note: values below are standard examples from ISO 2768‑1 (rounding to shown digits). Confirm with the published standard for production use.
ISO 2768 is an international standard developed by the International Organization for Standardization (ISO) to regulate general tolerance requirements for mechanical parts. Its primary purpose is to simplify engineering drawings . Instead of cluttering a drawing with a tolerance value next to every single dimension, an engineer can add a single note — for example, "ISO 2768-mK" — in the title block. This single callout automatically defines the permissible variation for all features that do not carry an explicit individual tolerance. While there are other classes—such as "f" (fine)
) directly next to that specific dimension on the drawing. Specific callouts always override general standards. Best Practices for Designers and Machinists
6 to 30 mm: ±0.5 mm
End of examination.
However, it is not a magic wand. Always ask yourself: “If this dimension drifts by 0.2mm, will my assembly fail?” If the answer is yes, add a specific tolerance (e.g., 10.0 ±0.01mm ) directly next to that dimension.
The "K" component dictates the permissible deviations for form, orientation, and position. Like linear tolerances, these values scale with the size of the component (specifically, the length of the longer feature or the datum axis). Straightness and Flatness
Bearing seats, press fits, and dynamic sealing surfaces typically require tolerances tighter than . For these, specific ISO fit classes (e.g., ) must be manually explicitly written on the feature. Engineers and manufacturers should stay informed about these
ISO 2768 is an international standard that defines general tolerances for linear and angular dimensions, as well as geometric tolerances for features without individual tolerance indications. It simplifies technical drawings by eliminating the need to specify tolerances for every single dimension. is a combination of two parts of the standard:
Because it's an international standard, a part designed with ISO 2768-mK in Germany can be manufactured in Australia or the US with zero ambiguity. Breaking Down the Tables