General Tolerances

General tolerances refer to the permissible deviations in a part’s dimensions and shapes according to the ISO 2768 standard, when specific tolerances are not individually indicated on a drawing. Their purpose is to streamline design and manufacturing: not every measurement needs an individual tolerance, 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 deviations in length, width, diameters, and angles, for example.
• Geometric tolerances (ISO 2768-2) cover the geometric properties of a part, such as straightness, flatness, perpendicularity, and symmetry.

The standard defines different precision classes (f = fine, m = medium, c = coarse, v = very coarse) that specify how tight or loose the tolerances are. This allows you to choose the appropriate level based on the intended application: for example, precise mating surfaces of a machine require a finer class, while a coarser class is sufficient for larger, less critical parts.

General tolerances help ensure:

• that parts fit together without requiring unnecessarily precise manufacturing
• that manufacturing costs stay reasonable
• that designers and manufacturers have a shared understanding of the tolerance requirements

When a drawing includes a note such as ISO 2768-mK, it means that the medium (m) level is used for length and angular dimensions, and class K is used for shape and positional tolerances.

Linear Dimensions

General tolerances for linear dimensions specify how much the linear measurements of a part (e.g., length, width, diameter) can deviate from the nominal value. The classes range from fine (f) to very coarse (v), depending on the required precision. READ MORE

Broken edges (external radii and chamfer)

General tolerances for broken edges control how much the chamfers on edges can deviate from the designed measurement. This ensures edges function correctly during assembly and for safety purposes. READ MORE

Angular Dimensions

Angular dimensions refer to measurements such as 90° angles or other geometric angles. General tolerances determine how precisely these angles must be manufactured for parts to fit together without issues. READ MORE

Straightness and Flatness

Straightness tolerances relate to how straight a particular surface or edge is. Flatness tolerances, on the other hand, ensure that an entire surface remains flat enough without excessive waviness. READ MORE

Perpendicularity

Perpendicularity tolerances ensure that two surfaces or axes are at the correct angle (90°) to each other. This is important, for example, in mating surfaces and bearings. READ MORE

Symmetry

Symmetry tolerances specify how accurately the center line or plane of a part is positioned relative to opposite surfaces. Symmetry is especially important for rotating parts and for aesthetic structures. READ MORE

Circular Run-out

Circular Run-out tolerances are related to the motion of rotating parts. They define how much a shaft or surface can deviate from a perfect rotational movement. This affects issues like vibration and wear. READ MORE