Overview
ISO 22081:2021 - "Geometrical product specifications (GPS) - Geometrical tolerancing - General geometrical specifications and general size specifications" - defines rules for creating and interpreting general geometrical specifications and general size specifications used in technical product documentation (TPD). It provides a structured way to apply common tolerances across many integral features of a part (thereby reducing repetitive indication) while clarifying limits: it applies only to integral features (including features of size), linear or angular size dimensions, and does not cover derived features, integral lines, or non-linear/non-angular dimensions.
Key topics and requirements
- Scope and applicability
- Applies only to integral features as defined by ISO 17450-1.
- Excludes derived features, integral lines, and dimensions other than linear or angular (see ISO 14405 series).
- Indication in TPD
- General specifications must be clearly indicated (e.g., wording “General tolerances” with a reference to ISO 22081) in or near the title block or product definition dataset.
- Tolerance values can be single or variable (dependent on feature size or distance to the datum system using TEDs).
- Types of general specifications
- Two main types: general geometrical specifications and general size specifications (linear or angular).
- Rule: only the specification types listed in the standard’s tables (Tables 1 & 2) may be used to define general specifications.
- General geometrical specification format
- The standard requires the general geometrical specification to be indicated with a surface profile characteristic.
- Applicability exceptions
- General specs do not apply where an integral feature is:
- specified by an individual or general size specification;
- specified by an individual geometrical specification (or its derived feature);
- used as a datum in the datum system referenced by the general specification;
- represented only in simplified form (e.g., threads, fillets not modeled in CAD).
- Designer responsibilities
- Ensure functional requirements are captured, appropriate features are specified, and the overall part specification is complete and unambiguous.
Applications
- Streamlines drawings and 3D CAD datasets by applying consistent tolerances across multiple similar features.
- Useful for mechanical designers, CAD modelers, manufacturing and quality engineers, and technical drafters to:
- reduce annotation clutter in TPD,
- standardize tolerances across families of features,
- support inspection planning and contract requirements with clear general tolerancing rules.
- Supports both 2D drawing conventions and 3D model-based definition workflows (see ISO 16792 for CAD attachment rules).
Related standards
For implementation, reference the full ISO 22081:2021 text and consult your national standards body or ISO/TC 213 guidance.