Iso 2768 Mk — Norme

By invoking ISO 2768-mK, the designer communicates that all dimensions without specific tolerances must comply with the “medium” linear and “K” geometric limits. This drastically simplifies the drawing, reduces clerical errors, and streamlines the first-article inspection report. For the workshop, it signals a standard of good practice: the part must be reasonably flat, holes must be reasonably perpendicular to faces, and linear sizes must fall within typical milling or turning accuracy without secondary operations. However, ISO 2768-mK is not a universal panacea. It is explicitly not intended for certain features. The standard excludes tolerances for chamfer angularity, fillet radii, or dimensions that are inherently dependent on other features (e.g., angular relationships from a datum). Furthermore, “mK” is inadequate for high-precision industries like aerospace or medical devices, where finer classes (like ISO 2768-fH) or fully defined individual tolerances are mandatory.

Critically, the standard does not relieve the designer of responsibility. If a critical shaft-bore interface requires a clearance of 0.01 mm, relying on the “medium” tolerance of ±0.2 mm would lead to catastrophic failure. In such cases, a specific tolerance must be placed directly on the dimension, overriding the general standard. The note “ISO 2768-mK” applies only to the uncontrolled features. ISO 2768-mK is a masterpiece of engineering communication—a compact instruction that balances precision, cost, and clarity. The “m” guarantees that linear dimensions are held to a competent industrial standard, while the “K” ensures basic geometric integrity. For the vast majority of machined, cast, or 3D-printed components that do not require micron-level perfection, adopting ISO 2768-mK is a sign of mature engineering practice. It acknowledges that while perfection is a theoretical ideal, manufacturability and economy are the practical realities. When a drafter writes “ISO 2768-mK” in the title block, they are not being imprecise; they are being intelligently efficient, allowing the workshop to focus its precision only where it truly matters. norme iso 2768 mk