General tolerances

General tolerances are permissible deviations in a component’s dimensions and geometry according to the ISO 2768 standard when individual tolerances have not been specified separately on the drawing. Their purpose is to streamline design and manufacturing: not every dimension needs to be toleranced individually, as the general rules cover the most common cases.

General tolerances are divided into two main groups:

• Dimensional tolerances (ISO 2768-1) apply to linear dimensions and angles. These are used, for example, for deviations in length, width, diameters, and angles.
• Geometrical tolerances (ISO 2768-2) apply to the component’s geometric characteristics, such as surface straightness, flatness, perpendicularity, and symmetry.

The standard defines different accuracy classes (f = fine, m = medium, c = coarse, v = very coarse), which indicate how tight or loose the applicable tolerances are. This makes it possible to select an appropriate level according to the intended use: for example, precision mating surfaces in a machine require a finer class, while a coarser class is sufficient for larger, less critical components.

General tolerances help ensure:

• that components fit together without unnecessarily precise manufacturing
• that manufacturing costs remain reasonable
• that designers and manufacturers interpret the tolerance requirements consistently

When a designation such as ISO 2768-mK is added to a drawing, it means that the medium class (m) applies to linear and angular dimensions, while tolerance class K applies to geometrical tolerances.

Linear Dimensions

General tolerances for linear dimensions define how much a component’s linear dimensions (e.g., length, width, and diameter) may deviate from the nominal value. The classes range from fine (f) to very coarse (v), depending on the required accuracy. READ MORE

Chamfered Angles

General tolerances for chamfered angles specify how much the chamfers on edges may deviate from the designed dimensions. This helps ensure that the edges function correctly, for example during installation and with regard to operational safety. READ MORE

Angular Dimensions

Angular dimensions apply, for example, to 90° angles and other geometric angles. General tolerances define how accurately an angle must be manufactured so that components fit together without problems. READ MORE

Straightness and Flatness

Straightness tolerances apply to the straight line of an individual surface or edge. Flatness tolerances, in turn, ensure that the entire surface remains sufficiently flat and does not have excessive waviness. READ MORE

Perpendicularity

Perpendicularity tolerances ensure that two surfaces or axes are at the correct angle to each other. This is important, for example, for mating surfaces and bearing seats. READ MORE

Symmetry

Symmetry tolerances define how accurately a component’s centerline or center plane is positioned relative to opposing surfaces. Symmetry is particularly important in rotating components and aesthetically demanding structures. READ MORE

Runout

Runout tolerances relate to the motion of rotating components. They define how much an axis or surface may deviate from a perfect rotational movement. This affects, for example, vibration and wear. READ MORE