SIST EN ISO 21204:2020 PDF

Overview

SIST EN ISO 21204:2020 - Geometrical product specifications (GPS) - Transition specification defines how to specify extended edge transition features that connect two adjacent integral features (for example, between two planes or between a cylinder and a plane nominally perpendicular to it). The standard establishes a set of specification operators, modifiers, and drawing indications (including the proportions and dimensions of graphical symbols) to communicate transition geometry in technical drawings and CAD. It is intended for relatively simple edge transition functions (e.g., ensuring assembly without interference); more complex functional requirements should use full geometrical tolerancing tools.

Key topics and technical requirements

• Edge transition definitions: Extended edge transition features include portions of adjacent features and apply to any line in a defined direction in the transition area. Corners (transitions between three or more features) are explicitly excluded.
• Scope limitation: The standard is intentionally limited to transitions between two planes and between a cylinder and a plane nominally perpendicular to it.
• Profile types and boundaries: Specifications cover a range of profile forms and limits such as fixed, variable and consistent radius profiles, chamfers, elliptical profiles, and CAD-defined profiles. It also defines maximum material and least material boundary specifications and combinations with profile specifications.
• Symbols and drawing indications: Graphical symbols, their proportions and dimensions, and rules for face-view and 3D indications are standardized to ensure consistent communication on drawings and models.
• Supplemental rules: Rules for tolerance zone extent, primary adjacent reference sections, multiple toleranced features, and “between” or “around” indications.
• Annexes: Informative Annex A gives a preliminary algorithm for identifying toleranced features and adjacent reference sections (subject to future refinement). Annex C provides relations/dimensions of graphical symbols; Annex D relates this standard to the GPS matrix model.

Practical applications and users

Who uses this standard:

• Design and mechanical engineers specifying mating edges and transitions to avoid interference
• CAD modelers and technical drafters applying standardized drawing symbols and profile specifications
• Manufacturing and quality engineers inspecting edge transitions or verifying assembly fit
• Standards committees and technical documentation teams integrating GPS rules into workflows

Practical uses:

• Communicating simple transition geometry on engineering drawings and 3D CAD (fixed or variable radii, chamfers, elliptical blends)
• Defining manufacturing and inspection boundaries for edge transitions to ensure consistent assembly behavior

Related standards

• ISO 14638 (GPS matrix model)
• ISO 8015 (fundamental GPS rules)
• ISO 14253-1 (decision rules for verification)
• ISO/TC 213 publications on dimensional and geometrical product specifications

Keywords: SIST EN ISO 21204:2020, transition specification, geometrical product specifications, GPS, edge transition feature, radius profile, chamfer, CAD profile, drawing symbols, tolerancing.