ISO 8538:1999 PDF

Overview

ISO 8538:1999 defines the dimensions for aerospace hexagonal, self-locking nuts with a counterbore and captive washer using MJ threads. It covers nuts of classification 1 100 MPa (ambient)/235 °C, 1 100 MPa (ambient)/315 °C, and 1 100 MPa (ambient)/425 °C. This International Standard is intended for the compilation of aerospace product standards and provides dimensional requirements to support procurement and manufacturing compliance.

Key topics and requirements

• Scope: Dimensional specification for self-locking hexagonal nuts with counterbore and captive washer (MJ threads) for specified strength/temperature classifications.
• Dimensions and tolerances: All dimensions and tolerances are given in millimetres. Values apply after any surface coating(s) but before lubricant application.
• Threading: MJ thread limits and basic fit are referenced to ISO 5855‑2. Thread tolerances in the self-locking zone apply before forming out-of-round.
• Self-locking feature: Achieved by localized out-of-round form in the nut (tooling marks permissible in that area). The captive washer must be free to rotate on the nut.
• Form and position tolerances: Conform to ISO 8788 (tolerances of form and position for nuts).
• Compatibility: Dimensions were determined to satisfy the procurement specification ISO 5858 (self-locking nuts with maximum operating temperature ≤ 425 °C).
• Product configuration: Figure and table layouts define key dimensions (bearing diameter, wrench engagement, chamfer, etc.) and include notes on surface texture and manufacturing discretion where details are not specified.

Applications and users

• Who uses ISO 8538:
  • Aerospace design and structural engineers specifying fasteners for airframes, engines, and high-temperature assemblies.
  • Fastener manufacturers producing MJ-thread hex nuts with captive washers.
  • Quality and inspection teams verifying dimensional conformity.
  • Procurement specialists and standards writers compiling aerospace product standards.
• Practical applications:
  • High-temperature aerospace joints where self-locking capability and captive washer retention are required.
  • Components exposed to elevated temperatures (up to classification limits) in propulsion, bleed air systems, and hot-structure assemblies.
  • Standardizing parts lists and procurement documents to ensure interchangeability and traceability.

Related standards

• ISO 5855‑2 - MJ threads: limit dimensions for bolts and nuts.
• ISO 5858 - Procurement specification for self-locking nuts (≤ 425 °C).
• ISO 8788 - Fastener tolerances of form and position.

Keywords: ISO 8538:1999, aerospace nuts, hexagonal self-locking nuts, MJ threads, captive washer, counterbore, dimensions, high-temperature fasteners, aerospace standards.