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Tolerance classes according to ISO 22081 and DIN ISO 2768: Optimal use of general tolerances
This article addresses the topic of general tolerances and their tasks in the design process.
Tolerances are an essential component in the production of mechanically moving parts, as they ensure that components interact correctly. General tolerances and their tolerance classes help to simplify drawings.
The tolerances are specified in the DIN ISO 2768 standard. Many designers use general tolerances as a simplified variation of tolerances to make the design process easier.
What are tolerances in design?
Tolerances in design are generally defined as the deviation of a parameter from its ideal value. This deviation is divided into tolerance classes that determine the potential impacts of the deviation. DIN ISO 2768 specifies which tolerances are appropriate for which applications.
The most important terms are:
- Nominal dimension
- Upper tolerance (+/-), also called maximum dimension
- Lower tolerance (+/-), also called minimum dimension
- Limit
- Fit: Is the dimensional relationship (way of interaction) between two components. For example, how do a bearing and a shaft fit together; how much "play" is there between the two components.
The tolerance with upper and lower deviation is also colloquially referred to as the tolerance limit.
DIN ISO 2768 applies to mechanically manufactured parts, which describes the following characteristics:
- for lengths, broken edges and diameters
- for angles
- for concentricity and axial runout
- for shape and position
- for symmetry
- for perpendicularity
- for evenness and straightness
DIN ISO 2768 is being replaced by the new ISO 22081 in future.
Tolerance according to ISO 22081
As a designer, ISO 22081 enables you to optimally simplify product specifications and proof of conformity and to fully describe all non-functional characteristics, taking into account production-related and material-physical characteristics. Careful application of the general tolerances can help to simplify the design process and ensure that the results meet the requirements.
Designers using ISO 22081 must make optimal use of the general tolerance classes and the general geometrical specifications. Instead of specifying set tolerance values, ISO 22081 only determines the specified characteristic:
- Characteristic for position
- Characteristic for surface profile
- Characteristic for line profile
- Characteristic for overall runout and concentricity
- Characteristic for straightness
- Characteristic for symmetry
- Characteristic for perpendicularity
- Characteristic for position and shape
- Characteristic for evenness
- Characteristic for distance
- Characteristic for parallelism
- Characteristic for coaxiality
- Characteristic for concentricity
- Characteristic for inclination and angles
- Characteristic for roundness
The user must then decide which tolerance value (constant or variable) is best suited for implementing the characteristic and also define the mandatory complete reference system with all tolerated nominal geometric elements.
NOTE Complete, clear product documentation and product conformity is essential to fulfil the requirements of increasing global cooperation and outsourcing. As a designer, it is important to be familiar with the tolerance classes and ISO 22081 so they can be used optimally in the design.
What must be considered when using DIN ISO 22081?
If you, as a designer, want to use tolerance classes and DIN ISO 22081 optimally, you should take the following exclusion criteria into account to rule out ambiguities. The most important exceptions are outlined below:
- DIN ISO 22081 does not apply to all integral geometric elements derived from integral size dimension elements that can be used with individual geometric specifications. These are defined either directly in the technical product documentation or indirectly via CAD attributes in the digital data set for product definition.
- DIN ISO 22081 does not apply to linear size dimension elements or sections of linear size dimension elements that are subject to a general dimension specification or have an individual dimension specification defined directly in the technical product documentation or indirectly via CAD attributes in the digital data set for the product definition.
- It is important to note that ISO 22081 does not apply to the reference elements defined in the tolerance indicator’s reference field of the general geometrical specification.
Tolerances according to DIN ISO 22081
The International Standardisation Organisation (ISO) has developed DIN ISO 22081 for tolerance classes in design and mechanical engineering. DIN ISO 22081 comprises four basic tolerances: the fit tolerance, the geometrical tolerance, the dimensional tolerance and the position and alignment tolerance.
The fit tolerance defines the dimensions and fits that must be taken into account during component assembly. It also determines how narrow the gap between the parts can be.
The geometrical tolerance defines the shape and size of certain components and ensures that they have the required accuracy.
Dimensional tolerance refers to the dimensions and tolerances of a component and is used to minimise the impacts of undesired deviations during the manufacture of components.
The position and alignment tolerance controls the direction and position in which a component must be mounted to achieve a specific accuracy.
Important things to note for the DIN ISO 2768 standard
New international standards for general tolerances were introduced at the end of 2022. DIN ISO 22081 will soon replace the old standard DIN ISO 2768.
The old standard DIN ISO 2768 is still valid (as at March 2023) and can therefore continue to be used.
For new designs, it is advisable to use the new standard DIN ISO 22081.
As a Japanese manufacturer, MISUMI manufactures its products according to the Japanese standard JIS B0401 which is equivalent to the ISO 22081 standard.
Selecting the appropriate tolerance class and what needs to be considered
The general tolerances are divided into classes.
The following factors must be weighed up during the design and construction process:
- Required accuracy of fit
- Costs
IMPORTANT The tolerance class also determines how complex the production or procurement of the component will be. In all cases, the lower the tolerance, the higher the costs will be
The general tolerances are divided into:
- f (fine) – e.g. precision engineering
- m (medium) – e.g. mechanical engineering (standard workshop accuracy)
- c (coarse) – e.g. foundry technology
- v (very coarse) – hardly used today, as modern manufacturing processes enable higher accuracy
How are tolerances and tolerance classes added and represented in the technical drawing?
An abbreviation in the title block of a technical drawing indicates the tolerance for the entire drawing. The exact specifications are described in the standards DIN 406-10 and DIN 406-11.
For instance:
- DIN ISO 2768-m (for medium)
- General tolerance DIN ISO 2768-c (for coarse)
In CAD programmes, the set tolerances are displayed automatically and do not need to be inserted manually.
What other tolerances need to be observed?
DIN ISO 2768 and ISO 22081 apply for mechanically manufactured parts.
Different standards apply for other manufacturing processes, for example:
- DIN 16742 for injection-moulded parts
- DIN 12020 for the production of aluminium profiles
- ISO 20457 for plastic parts
Quality control for tolerances and parts – how to achieve precise results
As manufacturers, we know how important it is that the components we design and produce meet the highest quality standards. Measuring tolerances is an important part of our quality control.
By using different tolerances, a component can be manufactured for you so that is meets the design requirements.
As a Japanese manufacturer, MISUMI manufactures its products according to JIS B0401, which is equivalent to ISO 22081.
MISUMI uses the extremely precise tolerances h5/g6 for many components. For further information, use our tolerance tables according to JIS B0401-1, -2 (1998).
Tolerance tables for dimensions in accordance with DIN ISO 2768-1
Limit tolerances for angular dimensions
| Tolerance class | Limit tolerances in angular units for nominal dimension range of the shortest side in mm | ||||
|---|---|---|---|---|---|
| up to 10 | above 10 to 50 | above 50 to 120 | above 120 to 400 | above 400 | |
| f (fine) | ± 1 ° | ± 30 ’ | ± 20 ’ | ± 10 ’ | ± 5 ’ |
| m (medium) | ± 1 ° | ± 30 ’ | ± 20 ’ | ± 10 ’ | ± 5 ’ |
| c (coarse) | ± 1 ° 30 ’ | ± 1 ° | ± 30 ’ | ± 15 ’ | ± 10 ’ |
| v (very coarse) | ± 3 ° | ± 2 ° | ± 1 ° | ± 30 ’ | ± 20 ’ |
Limit tolerances for length dimensions (not for broken edges)
| Tolerance class | Limit tolerances in mm for nominal dimension range in mm | |||||||||
|---|---|---|---|---|---|---|---|---|---|---|
| up to 0.5 | 0.5 to 3 | above 3 to 6 | above 6 to 30 | above 30 to 120 | above 120 to 400 | above 400 to 1000 | above 1000 to 2000 | above 2000 to 4000 | above 4000 to 8000 | |
| f (fine) | see note | ± 0.05 | ± 0.05 | ± 0.10 | ± 0.15 | ± 0.2 | ± 0.3 | ± 0.5 | - | - |
| m (medium) | see note | ± 0.10 | ± 0.10 | ± 0.20 | ± 0.30 | ± 0.5 | ± 0.8 | ± 1.2 | ± 2 | ± 3 |
| c (coarse) | see note | ± 0.20 | ± 0.30 | ± 0.50 | ± 0.80 | ± 1.2 | ± 2.0 | ± 3.0 | ± 4 | ± 5 |
| v (very coarse) | see note | - | ± 0.50 | ± 1.00 | ± 1.50 | ± 2.5 | ± 4.0 | ± 6.0 | ± 8 | ± 12 |
Note For nominal dimensions smaller than 0.5 mm, the limit tolerances must be specified directly on the relevant nominal dimension.
Limit tolerances for broken edges (rounding radius and chamfer heights)
| Tolerance class | Limit tolerances in mm for nominal dimension range in mm | |||||
|---|---|---|---|---|---|---|
| Up to 0.5 | 0,5 to 3 | above 3 to 6 | above 6 to 30 | above 30 to 120 | above 120 to 400 | |
| f (fein) | see note | ± 0.2 | ± 0.5 | ± 1.0 | ± 2.0 | ± 4.0 |
| m (medium) | see note | ± 0.2 | ± 0.5 | ± 1.0 | ± 2.0 | ± 4.0 |
| c (coarse) | see note | ± 0.4 | ± 1.0 | ± 2,0 | ± 4.0 | ± 8.0 |
| v (very coarse) | see note | ± 0.4 | ± 1.0 | ± 2.0 | ± 4.0 | ± 8.0 |
Note For nominal dimensions smaller than 0.5 mm, the limit tolerances must be specified directly on the relevant nominal dimension.
Tolerance tables for shape and position in accordance with DIN ISO 2768-2
DIN ISO 2768-2 specifies the shape and position tolerances.
Tolerances for straightness and evenness
| Tolerance class | General tolerances for straightness and evenness in mm for nominal dimension range mm | |||||
|---|---|---|---|---|---|---|
| up to 10 | above 10 to 30 | above 30 to 100 | above 100 to 300 | above 300 to 1000 | above 1000 to 3000 | |
| H | 0.02 | 0.05 | 0.1 | 0.2 | 0.3 | 0.4 |
| K | 0.05 | 0.1 | 0.2 | 0.4 | 0.6 | 0.8 |
| L | 0.1 | 0.2 | 0.4 | 0.8 | 1.2 | 1.6 |
Tolerances for perpendicularity
| Tolerance class | General tolerances for perpendicularity in mm for nominal dimension range mm | |||||
|---|---|---|---|---|---|---|
| up to 100 | above 100 to 300 | above 300 to 1000 | above 1000 to 3000 | |||
| H | 0.2 | 0.3 | 0.4 | 0.5 | ||
| K | 0.4 | 0.6 | 0.8 | 1.0 | ||
| L | 0.6 | 1.0 | 1.5 | 2.0 | ||
Tolerances for symmetry
| Tolerance class | General tolerances for symmetry in mm for nominal dimension range mm | |||||
|---|---|---|---|---|---|---|
| up to 100 | above 100 to 300 | above 300 to 1000 | above 1000 to 3000 | |||
| H | 0.5 | 0.5 | 0.5 | 0.5 | ||
| K | 0.6 | 0.6 | 0.8 | 1.0 | ||
| L | 0.6 | 1.0 | 1.5 | 2.0 | ||
Configure your components
You can configure shafts and other components freely with the MISUMI configurator.
Select the component type and set the desired specifications and characteristics.
To deviate from the general tolerances, you can narrow your selection further here via our options tables for shaft and shank tolerances.
CAD library
Use our extensive CAD library to select the optimal part for your components and applications.
Find inspiration in our inCAD library and edit your designs with our SolidWorks add-on “inCADcomponents”.
