Overview
ISO 5458:2018 - Geometrical product specifications (GPS) - Geometrical tolerancing - Pattern and combined geometrical specification - provides complementary rules to ISO 1101 for defining and applying pattern specifications and combined geometrical specifications. The standard explains how to group multiple tolerance zones into a tolerance zone pattern and how to combine individual geometrical specifications (POSITION, SYMMETRY, LINE PROFILE, SURFACE PROFILE, and - when applicable - STRAIGHTNESS and FLATNESS) using the CZ, CZR and SIM modifiers.
Key topics and technical requirements
- Pattern specification concept: Defines a pattern specification as a combined requirement controlled by a set of geometrical specifications and a tolerance zone pattern (see Annex C for examples).
- Tolerance zone pattern: A combination of multiple tolerance zones with internal constraints (location and/or orientation) that can also have external constraints referencing a datum system.
- Specification modifiers:
- CZ / CZR - modifiers for single-indicator pattern specifications (combined zones or combined-rotation-only zones).
- SIMn - modifier for multiple-indicator (simultaneous) pattern specifications; the index n can identify simultaneous requirement groups.
- SZ / UF - modifiers for separate zones and united features where relevant.
- Pattern types:
- Single indicator pattern specification - one tolerance indicator controls a grouped set of features.
- Multiple indicator pattern specification - more than one indicator, with simultaneous requirements applied.
- Multi-level single indicator - single indicator applied to multiple groups of toleranced features.
- Principles and rules: Complements ISO 1101 and ISO 8015 by clarifying independence vs. simultaneity of specifications, and provides specific rules (A–E) for position and pattern specifications.
- Scope exclusions: Does not cover least and maximum material requirement applications (see ISO 2692) or establishment of common datum systems based on pattern features (see ISO 5459).
Practical applications and users
ISO 5458:2018 is intended for engineers and professionals involved in:
- Mechanical design and tolerancing of feature groups (e.g., repetitive features or arrays).
- CAD/CAM modelling where pattern tolerancing must be represented and validated.
- Quality engineering, inspection and metrology for verifying combined geometric requirements.
- Drafting and technical documentation to ensure unambiguous 2D drawing and model specifications.
Using ISO 5458 helps ensure consistent interpretation of grouped tolerances, reduce assembly issues, and support robust inspection plans when multiple features must meet relational constraints.
Related standards
- ISO 1101 - Geometrical tolerancing general rules (primary complement).
- ISO 8015 - GPS fundamentals (principles and rules).
- ISO 5459 - Datum systems (external constraints).
- ISO 2692 - Least and maximum material requirements (excluded from ISO 5458 use).
Keywords: ISO 5458:2018, GPS, geometrical tolerancing, pattern specification, CZ, CZR, SIM modifier, combined geometrical specification.