Overview
ISO 15872:2017 - Aerospace - UNJ threads - Gauging defines accepted methods for inspecting and gauging ISO UNJ threads (threads specified in ISO 3161) used in aerospace applications. The standard specifies gauge types, gauge function and design, setting procedures, environmental requirements (reference temperature per ISO 1) and procedures for evaluating major, pitch and minor thread diameters. Alternative measurement methods are permitted only when correlated to the specified gauges.
Key SEO terms: ISO 15872:2017, UNJ threads gauging, aerospace thread gauges, ISO 3161.
Key topics and requirements
- Scope and normative references: Applies to gauging of ISO UNJ threads; normative references include ISO 3161 (thread dimensions) and ISO 1 (reference temperature).
- Terms and definitions: Uses standard metrology definitions (e.g., virtual pitch diameter, simple pitch diameter, best wire size) to ensure consistent measurement language.
- Types of gauges:
- GO screw ring gauges and GO/NOT GO screw plug gauges
- Virtual pitch diameter indicating gauges (segments or rolls, two- or three-contact designs)
- Simple pitch diameter indicating gauges
- Major and minor diameter gauges (plain ring, plain calliper, point-contact)
- Optical comparator checks for root radius and minor diameter
- Gauge design and use: Details on gauge contact geometry, engagement length (e.g., ring length equal to nine pitches or basic major diameter, whichever is smaller), and requirements to account for form variations (pitch, helix, flank and roundness).
- Setting and calibration: Procedures for setting indicating gauges using setting plugs; requirement for correlation if other measurement systems are used.
- Reference temperature: Gauging should be performed at 20 °C. If product and gauge differ in thermal expansion, limits apply: 20 °C ±2 °C for sizes 1,000 UNJ and smaller; 20 °C ±1 °C for larger threads.
Practical applications and who uses ISO 15872:2017
- Aerospace fastener manufacturers and designers - to ensure thread conformity during production.
- Quality assurance and inspection engineers - for acceptance testing and in-process inspection of UNJ threaded components.
- Metrology labs and calibration service providers - to manufacture and certify GO/NOT GO and indicating gauges to aerospace requirements.
- Procurement, regulatory and conformity-assessment teams - to reference standardized gauging methods in contracts and quality plans.
Related standards
- ISO 3161 - Aerospace - UNJ threads - General requirements and limit dimensions (primary dimensional reference)
- ISO 1 - Standard reference temperature for dimensional measurements
- ISO 5408 - Terminology referenced by ISO 15872
- ASME B1.2 - Additional guidance (adjustable GO ring gauges / setting plug designs)
ISO 15872:2017 is essential for maintaining consistent, repeatable gauging practices for UNJ threads in critical aerospace assemblies.
