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Symmetry ensures that two features on a part are evenly spaced relative to a central datum plane or axis. Under class K, symmetry is tied to the longest feature: Nominal Length Range (mm) Symmetry Tolerance (mm) over 100 to 300 over 300 to 1000 over 1000 to 3000 Run-Out (Circular Run-out)
While Part 1 focuses on size, governs the shape and orientation of features. The "K" class is stricter than "H" but less stringent than "L". The 'K' class applies specifically to:
The title block of all engineering drawings shall contain the following note: general tolerance iso 2768-mk
The Basics of General Tolerance Standard – ISO 2768-mK - Eurotools
The "mK" combination is a popular default. The 'm' class provides good precision for most CNC-machined and sheet metal parts without demanding excessively tight (and expensive) controls. The 'K' class for geometric tolerances offers a solid middle ground, ensuring parts are straight and flat enough for proper assembly while being easily achievable by standard machine tools.
[Name], Lead Engineer Date: ___________
| 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' |
ISO 2768-1 defines four precision levels. The lower-case letter in "mK" stands for Medium .
Limits are based on the length of the longest surface line or diameter. Perpendicularity: Controls the 90-degree relationship between surfaces. This public link is valid for 7 days
Circular run-out controls the variation of a surface during a full 360-degree rotation around a datum axis. For class K, the circular run-out tolerance is fixed at maximum, regardless of the size of the component. Why Use ISO 2768-mK in Engineering?
Implementing this standard provides several clear operational advantages for engineering teams and machine shops alike:
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. Can’t copy the link right now
The "K" class defines general limits for the form and position of features. For example, surfaces with fitting dimensions must remain flat and parallel within the specified K-class range to ensure assembly functionality. 4. Technical Advantages