Instead of cluttering a drawing with ±0.1mm for every hole or slot, you write the standard once in the title block. This tells the workshop: “If no specific tolerance is shown next to a dimension, follow this table.”
The first letter refers to (Linear & Angular tolerances). There are four classes:
, covering geometrical tolerances like straightness, flatness, and perpendicularity. 1. ISO 2768-1: Linear Dimensions (Class m)
Any feature that directly impacts the structural integrity, safety, or legal compliance of a product should have an explicitly defined and inspected tolerance. Conclusion
: By referencing ISO 2768-MK on engineering drawings, specific tolerances do not need to be called out for every dimension, making drawings cleaner and easier to read. general tolerance iso 2768-mk
What you are using (CNC machining, sheet metal, injection molding)? What materials you are working with? Whether the part has any critical mating interfaces ? Share public link
Critical fits—such as a shaft pressing into a bearing—usually require tolerances much tighter than what class "m" provides. Always explicitly specify tight tolerances for functional mating surfaces.
Because it is an international ISO standard, a drawing created in Germany using ISO 2768-mK can be accurately interpreted and manufactured by a machine shop in Japan or the United States without communication barriers. Limitations: When Not to Rely on ISO 2768-mK
ISO 2768 is an international standard that provides for linear and angular dimensions, as well as geometrical features, of machined components. It simplifies drawings by establishing standard acceptable variations for features that do not have specific tolerances written next to them. The standard is split into two distinct parts: Instead of cluttering a drawing with ±0
For a shaft, this is how much it can deviate from a perfect straight line. For a flat surface, this is how much it can deviate from a perfect plane.
To solve this problem, the International Organization for Standardization developed . This standard simplifies engineering drawings by establishing a set of standard generic tolerances. When you see "ISO 2768-mK" in a drawing title block, it dictates the baseline precision for the entire part. What Does ISO 2768-mK Mean?
Circular run-out tolerances under Class K are limited to a maximum variation of across the surface, regardless of the part's size. Why Use ISO 2768-mK?
Therefore, when you see in a drawing title block, it means the component must be manufactured to Medium linear tolerances and Medium geometric tolerances . ISO 2768-m (Part 1): Linear and Angular Dimensions What you are using (CNC machining, sheet metal,
This report provides a comprehensive overview of the international standard . This standard is utilized in mechanical engineering and manufacturing to simplify technical drawings. By applying general tolerances for linear and geometric dimensions, manufacturers can reduce drawing complexity while ensuring that parts remain functional and cost-effective.
Part 2 establishes three tolerance classes: H, K, and L. The "K" designation represents the middle tier. 1. Straightness and Flatness
: If you are manufacturing a shaft with a diameter of 50 mm and the drawing calls out ISO 2768-m , the permissible diameter tolerance is ±0.3 mm . This means the final part diameter must be between 49.7 mm and 50.3 mm .
Section C — Drawing interpretation and correction (20 marks) 10. (8) A drawing note reads “Tolerances: ISO 2768‑m”. The drawing also shows a critical hole Ø12 H7 (H7 tolerance explicitly shown). Explain which tolerance controls the hole and why. If the hole callout is Ø12 H7 with no additional notes, give the rationale whether ISO 2768 affects it. 11. (6) On an assembly drawing, a set of mating parts are dimensioned: shaft nominal Ø20 (no tolerance), mating bore nominal Ø20 (no tolerance); note reads ISO 2768‑mk. Is this acceptable for precision fit? Explain what the drawing should show to ensure a clearance fit of 0.02–0.05 mm. 12. (6) A supplier manufactured a part to k class tolerances though the drawing specified m class; the part’s critical dimension of 25 mm is out of tolerance for m but within k. Explain the likely consequences for assembly and recommended actions (3 points).
