The following limits apply to lengths, widths, diameters, and steps: Nominal Dimension Range (mm) Permissible Deviation (mm) ±0.1plus or minus 0.1 ±0.1plus or minus 0.1 ±0.2plus or minus 0.2 ±0.3plus or minus 0.3 ±0.5plus or minus 0.5 ±0.8plus or minus 0.8 ±1.2plus or minus 1.2 ±2.0plus or minus 2.0 Broken Edges (External Radii and Chamfers)
: Governed by ISO 2768-2 , this covers geometric characteristics like flatness, straightness, and circular runout. Tolerance Tables for ISO 2768-mk
ISO 2768-2 does not define a general tolerance for . If cylindricity is critical, it must be specifically indicated on the drawing using GD&T symbols (⌭).
This article provides a detailed overview of the ISO 2768-mK standard, explaining its components, application, and importance in machining and fabrication. What is ISO 2768-mK?
Engineers must remember that ISO 2768 is a safety net, not a replacement for critical design work: general tolerance iso 2768-mk
Ranges from 0.05 mm for features up to 10 mm, increasing to 0.8 mm for features up to 3000 mm. Perpendicularity:
ISO 2768-m uses a . As the nominal size of the dimension increases, the allowable tolerance window also widens. This mirrors real-world manufacturing physics, where maintaining a tight tolerance on a large part is significantly harder than on a small part.
The permissible deviations for linear dimensions under the 'm' class depend on the length of the feature: Dimension Length (mm) Permissible Deviation (mm) ('m' - Medium) Over 3 to 6 Over 6 to 30 Over 30 to 120 Over 120 to 400 Over 400 to 1000
To use the standard effectively, you need to know how the nominal size of a feature dictates its allowable deviation. Here is a look at the "m" and "K" standards: Linear Dimensions (ISO 2768-m) The following limits apply to lengths, widths, diameters,
For class K, the allowable symmetry variation is 0.6 mm for all sizes up to 3000 mm.
| 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 |
The designation "mK" combines two specific parts of the standard: "m" (Medium) : Refers to ISO 2768-1 , covering linear and angular dimensions. "K" (Medium) : Refers to ISO 2768-2
, which covers geometrical tolerances (straightness, flatness, perpendicularity, symmetry, and run-out). ISO 2768-1: Dimensional Tolerances (Class m) This article provides a detailed overview of the
(straightness, flatness, perpendicularity, symmetry, and circular run-out). Tolerance Tables for ISO 2768-mK All values are in millimeters (mm) unless otherwise stated. ALFA MIMtech 1. Linear Dimensions (Class m) Applies to external sizes, internal sizes, and diameters. Range (Nominal Size) Tolerance (±) 0.5 to 3 mm >3 to 6 mm >6 to 30 mm >30 to 120 mm >120 to 400 mm >400 to 1000 mm >1000 to 2000 mm >2000 to 4000 mm 2. External Radii and Chamfer Heights (Class m) Applies to broken edges and rounded corners. ALFA MIMtech Range (Nominal Size) Tolerance (±) 0.5 to 3 mm >3 to 6 mm 3. Angular Dimensions (Class m) Applies to angular measurements. ALFA MIMtech Length of Short Side Tolerance (±) Up to 10 mm >10 to 50 mm >50 to 120 mm >120 to 400 mm Over 400 mm 4. Geometrical Tolerances (Class K) Applies to the form and position of features. waterson.com Feature Type Range (Nominal Length) Straightness & Flatness Up to 10 / 30 / 100 / 300 / 1000 / 3000 mm 0.05 / 0.1 / 0.2 / 0.4 / 0.6 / 0.8 mm Perpendicularity Up to 100 / 300 / 1000 / 3000 mm 0.4 / 0.6 / 0.8 / 1.0 mm Up to 100 / 300 / 1000 / 3000 mm 0.6 / 0.6 / 0.8 / 1.0 mm Circular Run-out All lengths Important Considerations Understanding ISO 2768-mK Tolerances for Engineers
For a nominal size (the dimension on the drawing), the permissible deviation under class is: Nominal Size Range (mm) Tolerance (± mm) Over 3 to 6 Over 6 to 30 Over 30 to 120 Over 120 to 400 Over 400 to 1000 Data sourced from ZEISS Quality Forum . External Radii and Chamfer Heights (mm)
Eliminates the need to write ±0.X next to every single non-critical dimension, preventing visual clutter.