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represents the gold standard for general tolerances in modern mechanical engineering. It harmoniously blends the 'medium' linear tolerances with 'medium' geometric controls to produce parts that are both functional and economical.
ISO 2768 is divided into two parts. When a drawing is marked with "ISO 2768-mK", it implies compliance with both parts:
Imagine you have designed a batch of 50 steel shafts. According to the drawing, each shaft must have a diameter of and a length of 100 mm . After machining, you measure the parts and find diameters ranging from 47.8 mm to 52.5 mm.
: Engineers write the code in the title block rather than calculating every margin.
Implementing this standard provides several clear operational advantages for engineering teams and machine shops alike: general tolerance iso 2768-mk
Circular run-out controls the cumulative variation of roundness and coaxiality when a part is rotated 360 degrees around an axis. Under , the maximum permissible circular run-out is 0.2 mm . Why Use ISO 2768-mK?
You cannot combine classes from different parts arbitrarily in a single shorthand. For example, "ISO 2768-mL" would mean linear class 'm' and geometric class 'L', which is unusual. Always use 'mk' for standard work.
If you are a machinist or quality inspector, seeing "ISO 2768-mk" on a drawing tells you:
These values are determined based on the length of the longest surface line or the nominal length of the surface. Nominal Length Range (mm) Flatness/Straightness Tolerance Class K (mm) 100 to 300 300 to 1000 1000 to 3000 2. Perpendicularity represents the gold standard for general tolerances in
is an international standard used to define "general tolerances" for manufacturing. By adding this single note to a technical drawing's title block, an engineer sets a default permissible variation for every dimension that doesn't have an explicit tolerance.
Governs linear and angular dimensions (e.g., lengths, radii, diameters, and angles).
: Governed by ISO 2768-1 , this defines permissible deviations for linear and angular dimensions, such as lengths, radii, and chamfers.
Instead of detailing a tolerance for every single hole, slot, and edge, an engineer can leave non-critical dimensions blank. The title block note ( General Tolerances: ISO 2768-mk ) automatically covers them. When a drawing is marked with "ISO 2768-mK",
| Nominal Length Range (mm) | Permissible Deviation (±mm) | | :--- | :--- | | 0.5 up to 3 | ±0.1 | | over 3 up to 6 | ±0.1 | | over 6 up to 30 | ±0.2 | | over 30 up to 120 | ±0.3 | | over 120 up to 400 | ±0.5 | | over 400 up to 1000 | ±0.8 | | over 1000 up to 2000 | ±1.2 |
For the 'm' class, the allowable deviation depends on the size of the dimension: Nominal Size (mm) Tolerance (± mm) 120 to 400 400 to 1000 External Radii and Chamfer Heights Nominal Size (mm) Tolerance (± mm) ISO 2768-2: Geometrical Tolerances (The 'k')
In manufacturing and mechanical engineering, technical drawings must specify exactly how much variation is allowed for every dimension. Specifying individual tolerances for hundreds of dimensions on a single drawing is incredibly time-consuming and creates cluttered, unreadable blueprints.
The designation indicates that a drawing follows medium accuracy limits for linear dimensions (class m) and medium geometric constraints (class K). It serves as a vital bridge between engineering intent and cost-efficient manufacturing.