Overview
ISO 8642:2025 - "Aerospace - Self-locking nuts with maximum operating temperature greater than 425 °C - Test methods" specifies standardized test methods for metric self-locking nuts with MJ threads intended for high‑temperature aerospace service (>425 °C). The standard describes required test devices and step‑by‑step methods for each inspection and applies when referenced by dimensional standards, product specifications, drawings or procurement documents. This is the third edition (replacing ISO 8642:2008).
Key topics and technical requirements
The document defines a comprehensive test suite used to verify mechanical, dimensional and locking performance of high‑temperature self‑locking nuts. Key test topics include:
- Hardness testing - Rockwell, Rockwell superficial and Vickers (HV 5 to HV 100) according to ISO 6508‑1 and ISO 6507‑1; measurement zones, minimum specimen thickness (≥10× penetration depth) and parallelism (≤3°). Note: nuts tested for hardness shall not be reused.
- Bearing surface squareness - mandrel, sliding collar and feeler gauge method to assess out‑of‑squareness against dimensional tolerances.
- Axial load and push‑out tests - verification of retention and axial strength under load.
- Wrenching feature and torque‑out tests - evaluation of wrench fit, drive features and torque required to overcome self‑locking.
- Self‑locking torque - ambient and after heat‑soak at maximum operating temperature to confirm locking performance after thermal exposure.
- Permanent set and vibration tests - assessment of irreversible deformation and resistance to vibration‑induced loosening.
- No‑rotation (captive washer) and swaging tests - tests for specific nut configurations and attachment methods.
Each test section identifies the test device, lubrication and environmental conditions (ambient or heat‑soak), and acceptance checks.
Applications and who uses it
ISO 8642:2025 is essential for:
- Aerospace fastener manufacturers qualifying high‑temperature self‑locking nuts
- Quality assurance and metallurgical test laboratories performing acceptance and lot tests
- Design and mechanical engineers specifying fasteners for high‑temperature engine, exhaust or hot‑structure applications
- Procurement/specification writers and certification bodies ensuring traceable test methods
- MRO and airworthiness teams validating repair or replacement parts
Using ISO 8642 helps ensure consistent test methods, reduces risk of fastener failure in extreme thermal environments, and supports supplier conformity and procurement clarity.
Related standards
Normative references cited include:
Keywords: ISO 8642:2025, self‑locking nuts, aerospace test methods, high‑temperature fasteners, MJ threads, hardness test, torque‑out test, vibration test.