Overview
EN ISO 2692:2021 - Geometrical product specifications (GPS) - Geometrical tolerancing - Maximum material requirement (MMR), Least material requirement (LMR) and Reciprocity requirement (RPR) (ISO 2692:2021) defines how to apply maximum- and least-material concepts and the reciprocity modifier to linear features of size. It is a GPS standard intended to control combined size and geometry where the two are interdependent (for example: assembly fits or minimum wall thickness). The document applies only to linear features of cylindrical type or two parallel opposite planes type.
Key topics
- Scope and applicability
- Applies to features of size that are cylindrical or two parallel opposite planes.
- Threaded features are not covered by specific rules in this standard (use with caution).
- Maximum Material Requirement (MMR)
- Used to manage assemblability by accounting for worst‑case size and geometrical deviations (e.g., minimum assembly clearance when mating parts are at their maximum material size).
- May be specified indirectly (via virtual size concepts) or by direct indication of the maximum material virtual size.
- Least Material Requirement (LMR)
- Used to control functions such as minimum wall thickness or maximum slot width to protect part strength or function.
- Also can be applied via indirect virtual size determination or by direct indication.
- Reciprocity Requirement (RPR)
- Optional modifier used with MMR or LMR to allow enlargement of the size tolerance when the actual geometric deviation does not fully consume the maximum/least-material virtual condition.
- Modifiers and symbols
- The 2021 edition adds provisions for direct indication of virtual sizes and introduces use of additional symbols (e.g., SZ, CZ, SIM) to support multi-feature and simultaneous requirements.
- Decision rules & GPS integration
- Conforms with GPS terminology and is intended to work within the ISO/GPS framework and decision rules (e.g., ISO 8015, ISO 14253-1).
Applications
- Control of assemblies where size + geometric variation determine fit (MMR for assembly clearance).
- Ensuring minimum wall thickness or material‑related safety margins (LMR).
- Combining dimensional and geometrical controls into a single requirement to reflect actual functional intent.
- Drawing and specification practice for mechanical design, inspection callouts, and tolerance stack analysis.
Who uses this standard
- Mechanical designers and CAD engineers specifying tolerances
- Tolerancing and metrology specialists
- Manufacturing and quality engineers performing inspection and assembly verification
- Technical procurement and drawing reviewers in engineering and production environments
Related standards
Keywords: EN ISO 2692:2021, MMR, LMR, RPR, geometrical tolerancing, GPS, maximum material requirement, least material requirement, virtual condition, assemblability, minimum wall thickness.
