In manufacturing, perfection is impossible. Every part coming off a CNC mill, lathe, or sheet metal bender will have tiny variations in size and shape. If engineers had to specify an individual tolerance for every single dimension on a complex blueprint, drawings would become unreadable, and design time would skyrocket. This is where comes in.
When a design requires higher precision, a different standard can be selected.
The designation "ISO 2768-mK" is split into two distinct parts, each governing a different aspect of the part's geometry:
ISO 2768-2 defines three tolerance classes for geometrical features, designated by the letters H, K, and L (with H being the tightest and L being the loosest). The . general tolerance iso 2768-mk
If a specific dimension has a directly applied tolerance (e.g., 10±0.05 ), the general tolerance ( ±0.2 for 10 mm) is for that feature. The individual tolerance takes precedence.
Note: For attributes like , Concentricity , and Parallelism , ISO 2768-2 directs users to rely on other fundamental geometric relationships (such as the envelope requirement or total run-out) rather than listing isolated general tolerance brackets. How to Implement ISO 2768-mk Correctly
ISO 2768-MK is a widely used international standard for general tolerances. It was published by the International Organization for Standardization (ISO) and provides a framework for defining general tolerances for linear and angular dimensions. In manufacturing, perfection is impossible
ISO 2768-mK is more than just a series of numbers on a chart; it is an essential communication tool that bridges the gap between design intent and manufacturing reality. Its notation provides a clear, efficient, and internationally understood definition of allowable deviations for non-critical dimensions on a part. By mastering the meaning of 'm' and 'K', engineers can produce cleaner drawings, manufacturers can work without ambiguity, and companies can ensure that their parts are produced cost-effectively to a standard of quality that is fit for purpose.
Let's look at exactly what the "m" and the "K" mean mathematically and how they govern the manufacturing process. 1. The Lowercase "m" (Linear and Angular Dimensions)
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ISO 2768-1 uses four classes: (fine), m (medium), c (coarse), and v (very coarse). The "m" class is the most common industry standard for CNC machining and general metalwork. Nominal Dimension Range (mm) Tolerance for "m" Class (mm) ±plus or minus Over 3 to 6 ±plus or minus Over 6 to 30 ±plus or minus Over 30 to 120 ±plus or minus Over 120 to 400 ±plus or minus Over 400 to 1000 ±plus or minus Data sourced from standard ISO 2768-1 charts . ISO 2768-2: General Geometrical Tolerances (The "K")
| Nominal Length of the Shorter Side (mm) | Permissible Deviation ('m' Class) | | :--- | :--- | | up to 10 | ±1° | | over 10 up to 50 | ±0°30' | | over 50 up to 120 | ±0°20' | | over 120 up to 400 | ±0°10' | | over 400 | ±0°5' |