Overview
EN ISO 3650:1998 - Geometrical product specifications (GPS) - Length standards - Gauge blocks defines the principal design and metrological characteristics for rectangular gauge blocks with nominal lengths from 0.5 mm to 1000 mm. It specifies limit deviations and tolerances for the calibration grade K and for grades 0, 1 and 2, and sets the measurement basis and traceability requirements that make gauge blocks suitable as primary length standards.
Key topics and technical requirements
- Scope and definitions: clear definitions for terms such as gauge block, central length, variation in length, flatness deviation and wringing.
- Metrological basis & traceability:
- Unit of length tied to the metre (SI definition).
- Traceability chain required to national/international length standards; interferometric calibration is the reference method.
- Reference conditions: 20 °C (ISO 1) and standard pressure 101 325 Pa.
- Reference orientation:
- For blocks ≤ 100 mm: vertical orientation (measuring faces horizontal).
- For blocks > 100 mm: horizontal orientation with specified support positions (supports at 0.211 × nominal length from ends).
- Material & thermal properties:
- Made of hardened steel or similarly wear‑resistant materials capable of wringing.
- Steel coefficient of thermal expansion specified for 10 °C–30 °C (document: (11.5 ± 1.0) × 10^-6 K^-1); values and uncertainties for non‑steel materials must be supplied.
- Geometrical tolerances & faces:
- Requirements for flatness, parallelism, perpendicularity, side-face geometry and edge conditions.
- Wringing behaviour and surface finish requirements to enable composite stacks.
- Calibration methods & documentation:
- Interferometry and comparison techniques described, including corrections, auxiliary plates and calibration certificates.
- Wringing test procedures and measurement uncertainty evaluation.
- Informative annexes: examples of comparison devices, relation to the GPS matrix model and bibliography.
Applications and users
- Calibration laboratories and national metrology institutes using gauge blocks as traceable length standards.
- Manufacturers of gauge blocks and precision measuring instruments.
- Quality/inspection departments in precision engineering and manufacturing requiring high-accuracy length references.
- Calibration service providers issuing certificates for length standards.
Related standards
- ISO 1 (reference temperature for length measurements)
- ISO 1101 (geometrical tolerancing)
- ISO 14253‑1 (inspection decision rules)
- VIM (International Vocabulary of Metrology)
Keywords: EN ISO 3650:1998, ISO 3650, gauge blocks, length standards, gauge block calibration, interferometry, metrological traceability, reference temperature 20°C, GPS.
