| Standard | Region | Key Difference | | :--- | :--- | :--- | | | International | Uses "m" for linear, "K" for geometry. | | DIN 7168 (Obsolete) | Germany | Replaced by ISO 2768. Do not use. | | ANSI Y14.5 | USA | Uses "General Tolerance Notes" (e.g., .X = ±.1, .XX = ±.01). Not metric-friendly. | | ISO 2768-cH | International | Coarse linear, High geometry (rarely used). |
The designation "mK" combines two specific tolerance classes from different parts of the ISO 2768 standard: m (Medium) : Defined in ISO 2768-1 , this class specifies permissible deviations for linear and angular dimensions (like lengths, radii, and diameters). K (Geometric) : Defined in ISO 2768-2 , this class specifies tolerances for geometrical features
ISO 2768 is an international standard created to simplify drawing specifications. it establishes for linear and angular dimensions without individual tolerance indications. The standard is divided into two parts:
| Nominal Length Range (mm) | f (Fine) | | c (Coarse) | v (Very Coarse) | | :--- | :--- | :--- | :--- | :--- | | 0.5 up to 3 | ±0.05 | ±0.1 | ±0.2 | – | | over 3 up to 6 | ±0.05 | ±0.1 | ±0.3 | ±0.5 | | over 6 up to 30 | ±0.1 | ±0.2 | ±0.5 | ±1.0 | | over 30 up to 120 | ±0.15 | ±0.3 | ±0.8 | ±1.5 | | over 120 up to 400 | ±0.2 | ±0.5 | ±1.2 | ±2.5 | | over 400 up to 1000 | ±0.3 | ±0.8 | ±2.0 | ±4.0 | | over 1000 up to 2000 | ±0.5 | ±1.2 | ±3.0 | ±6.0 | | over 2000 up to 4000 | – | ±2.0 | ±4.0 | ±8.0 | Tolerance Iso 2768 Mk Pdf
It removes the need to specify tolerances for every single dimension on a drawing, keeping it clean and readable.
The ISO 2768 MK PDF document provides detailed information on:
While you can use it, molded parts warp. Class "c" (Coarse) is often better for plastics. Class mK is ideal for metal after machining. | Standard | Region | Key Difference |
It keeps drawings clean. Engineers only need to specify tolerances for critical dimensions (like bearing fits), while "mk" handles the rest.
: Covers linear and angular dimensions. It features four tolerance classes: f (fine), m (medium), c (coarse), and v (very coarse).
This simple notation signals to the manufacturer that all unspecified dimensions are to be controlled according to the standard's allowances. The use of such notes is crucial as it removes ambiguity in the workshop and inspection department, ensuring that nothing is left to judgement. | | ANSI Y14
Specifically, the designation simplifies technical drawings by providing a standardized set of general tolerances for linear, angular, and geometrical dimensions. What is ISO 2768?
The free PDFs found online are reference copies . For a legal contract (e.g., aerospace or medical devices), you must purchase the official standard from ISO or your local national body (like ANSI or BSI).
While Part 1 deals with "size" (how long or wide something is), Part 2 deals with "shape" (how flat, straight, or square something is).
However, the overall length of the plate (200mm) is non-critical. You leave it blank. Because of , the machinist knows the 200mm length can vary by ±0.5mm. If the length comes back at 199.6mm, you cannot scrap the part. It is technically compliant.
So, when a drawing carries the specification , it is a shorthand instruction that says: "For any dimension that does not have an explicit tolerance, apply the Medium (m) tolerance table from Part 1 for its size, and the K tolerance table from Part 2 for its geometric characteristics".