Overview
ISO 1938-2:2017 - Geometrical product specifications (GPS) - Dimensional measuring equipment - Part 2: Reference disk gauges specifies the key metrological and design characteristics of reference disk gauges used for verifying the working size of gap gauges. The standard covers linear gauge sizes up to 500 mm and is part of the ISO/GPS family of standards that govern dimensional measurement and tolerance systems.
Key topics and technical requirements
- Scope and purpose: Defines what a reference disk gauge is and how it establishes the working size (WS) of a gap gauge used in pass/fail checking.
- Design characteristics: Two typical forms are described - full form cylindrical plug gauges (gauge type A) and segmental cylindrical bar gauges (gauge type B) - with design rules taken from ISO 1938-1 where applicable.
- Metrological characteristics: Focus on the gauge size S and form tolerances (for example, cylindricity). By default the two-point size (S) and a form deviation are required; additional characteristics can be specified by the user. Measurement modifiers follow ISO 14405-1 and geometric symbols from ISO 1101.
- Maximum permissible limits (MPL): Positions of tolerance limits for reference disk gauges relative to workpiece tolerance limits are defined (see Figure and Table references). The tolerance parameter H (and related values y, α, z) are used to calculate MPLs and are taken from Table 3 and ISO 286‑1 tolerance grades.
- Marking and traceability: Each reference disk gauge must be permanently marked with the workpiece size/tolerance (ISO code or numeric deviations), gauge type designation (ref. GO-M, ref. GO-U, ref. NO GO), serial number and manufacturer/trademark - marking must not affect gauging surfaces.
- Measurement conditions: The standard notes the influence of measuring force and elastic deflection - if verified without the standardized working load (e.g., on a CMM), deflection must be accounted for to determine the true WS (see informative Annex A).
Applications and users
ISO 1938-2:2017 is intended for:
- Gauge and fixture manufacturers designing and producing reference disk gauges.
- Calibration and metrology laboratories establishing traceable references for gap gauges.
- Quality engineers and inspection departments who specify or verify GO/NO GO gauges used in production inspection.
- Tooling designers and dimensional engineers applying GPS rules to size-control chains.
Practical uses include calibration of gap gauges, establishing wear limits, and ensuring consistent pass/fail inspection across production.
Related standards
Relevant GPS and metrology standards referenced include ISO 1938-1, ISO 14405-1, ISO 1101, ISO 286-1, ISO 17450-2, and measurement-uncertainty guides (GUM and VIM). ISO 1938-2 integrates with the GPS matrix and decision rules defined in ISO 8015 and ISO 14253-1.