ISO 2768 is widely applied across multiple industries, including CNC machining, to ensure consistent interpretation and application of tolerances. It is also aligned with DIN standards in Germany. By providing clear and measurable limits for dimensional variations and surface quality, ISO 2768 enables effective communication between manufacturers and customers. Compliance with this standard helps maintain quality control and ensures that parts meet required specifications.
The ISO 2768 standard is divided into two parts: ISO 2768-1 and ISO 2768-2.
ISO 2768-1 defines general tolerances for linear and angular dimensions. It offers multiple tolerance classes based on functional requirements, enabling standardized interpretation and application across different manufacturing scenarios.
ISO 2768-2 focuses on geometrical tolerances and surface characteristics. It establishes standardized tolerance classes to control form and positional deviations, ensuring consistency in surface quality and geometric accuracy across industries and production methods.
ISO 2768-1 simplifies technical drawings by introducing four general tolerance classes: fine (f), medium (m), coarse (c), and very coarse (v). It applies to a wide range of dimensions, including external and internal sizes, step dimensions, diameters, radii, distances, external radii, and chamfer heights.
Based on machining capability and design requirements, the appropriate tolerance class can be selected from standardized tolerance charts, ensuring a balance between precision, manufacturability, and cost efficiency.
|
Permissible deviations in mm for ranges in nominal lengths |
Tolerance Class Designation (Description) | |||
|---|---|---|---|---|
| f (fine) | m (medium) | 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 |
For nominal sizes below 0.5 mm, the deviations shall be indicated adjacent to the relevant
nominal size(s).
|
Permissible deviations in mm for ranges in nominal lengths |
Tolerance Class Designation (Description) | |||
|---|---|---|---|---|
| f (fine) | m (medium) | c (coarse) | v (very coarse) | |
| 0.5 up to 3 | ±0.2 | ±0.2 | ±0.4 | ±0.4 |
| over 3 up to 6 | ±0.5 | ±0.5 | ±1.0 | ±1.0 |
| over 6 | ±1.0 | ±1.0 | ±2.0 | ±2.0 |
For nominal sizes below 0.5 mm, the deviations shall be indicated adjacent to the relevantnominal size(s).
|
Permissible deviations in mm for ranges in nominal lengths |
Tolerance Class Designation (Description) | |||
|---|---|---|---|---|
| f (fine) |
m (medium) |
c (coarse) |
v (very coarse) |
|
| up to 10 | ±1° | ±1° | ±1°30′ | ±3° |
| over 10 up to 50 | ±0°30′ | ±0°30′ | ±1° | ±2° |
| over 50 up to 120 | ±0°20′ | ±0°20′ | ±0°30′ | ±1° |
| over 120 up to 400 | ±0°10′ | ±0°10′ | ±0°20′ | ±0°30′ |
| over 400 | ±0°5′ | ±0°5′ | ±0°10′ | ±0°20′ |
ISO 2768-2 is designed to simplify technical drawings by providing general geometrical tolerances classified into three tolerance classes: H, K, and L. This standard covers general geometric tolerances, including flatness, straightness, circularity, and cylindricity.
Similar to ISO 2768-1, ISO 2768-2 defines general tolerance ranges and permissible deviations. However, the key difference lies in how these deviations are defined and applied.
Table 2.1 specifies general tolerances for straightness and flatness. To determine the appropriate tolerance value, the length of the considered line is used for straightness, while for flatness, the longer edge length of the surface or the diameter of a circular feature is taken into account.
The general tolerance for circularity is equal to the value of the diameter tolerance. However, it must not exceed the concentricity tolerance specified in Table 2.1.
A specific general tolerance for cylindricity is not defined in relation to circularity.
The general tolerance for parallelism is equal to the dimensional tolerance, or the flatness/straightness tolerance, whichever is greater.
| Ranges of nominal lengths in mm | Tolerance Class | ||
|---|---|---|---|
| H | K | L | |
| up to 10 | 0.02 | 0.05 | 0.1 |
| above 10 to 30 | 0.05 | 0.1 | 0.2 |
| above 30 to 100 | 0.1 | 0.2 | 0.4 |
| above 100 to 300 | 0.2 | 0.4 | 0.8 |
| above 300 to 1000 | 0.3 | 0.6 | 1.2 |
| above 1000 to 3000 | 0.4 | 0.8 | 1.6 |
| Ranges of nominal lengths in mm | Tolerance Class | ||
|---|---|---|---|
| H | K | L | |
| up to 10 | 0.2 | 0.4 | 0.6 |
| above 10 to 30 | 0.3 | 0.6 | 1.0 |
| above 30 to 100 | 0.4 | 0.8 | 1.5 |
| above 100 to 300 | 0.5 | 1.0 | 2.0 |
| Ranges of nominal lengths in mm | Tolerance Class | ||
|---|---|---|---|
| H | K | L | |
| up to 10 | 0.5 | 0.6 | 0.6 |
| above 10 to 30 | 0.5 | 0.6 | 1.0 |
| above 30 to 100 | 0.5 | 0.8 | 1.5 |
| above 100 to 300 | 0.5 | 1.0 | 2.0 |
| Ranges of nominal lengths in mm | Tolerance Class | ||
|---|---|---|---|
| H | K | L | |
| 0.1 | 0.2 | 0.5 | |
If general tolerances in accordance with ISO 2768 are used in combination with the general tolerances of ISO 2768-1, the following should be indicated in the title block of the drawing or nearby:
a) ISO 2768
b) The tolerance class in accordance with ISO 2768-1;
c) The tolerance class specified in this part of ISO 2768.
Example: ISO 2768 – mK
In this case, the general tolerances for angular dimensions specified in ISO 2768-1 do not apply to non-referenced 90° angles, because ISO 2768-2 defines general tolerances for perpendicularity.
If the general dimensional tolerance (tolerance class m) is not applicable, the corresponding letter code may be omitted.
Example: ISO 2768-K
When the envelope condition “E” applies to all individual dimensional elements, the letter E becomes part of the general designation.
Example: ISO 2768 – mK-E
ISO 2768 covers widely used basic geometrical features and tolerances in manufacturing. It establishes tolerance values that help simplify design and production processes. However, it is important to note that there are other standards in the field of geometric dimensioning and tolerancing (GD&T), such as ASME Y14.5.
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Fiona Huang is a Sales Engineer with 16+ years of experience in the mechanical and precision manufacturing industry. She specializes in CNC machining components, custom fasteners, and engineering-driven manufacturing solutions. With strong expertise in international trade and technical project support, she focuses on transforming complex engineering requirements into high-precision, production-ready solutions for global clients.
