ISO 5858:1999

Overview

ISO 5858:1999 is an international procurement specification for metric self-locking nuts with MJ threads intended for aerospace use at a maximum operating temperature ≤ 425 °C. The standard specifies the required characteristics, inspection and test regimes, quality assurance, sampling plans and acceptance criteria for finished nuts. It is intended to be referenced in a nut’s definition document (drawing, national or in‑house standard) to make the requirements contractually binding.

Key topics and technical requirements

• Scope and applicability: Covers metric self‑locking nuts used in aerospace construction where operating temperature does not exceed 425 °C.
• Material and microstructure: Requires verification of material type (spectrographic/spectroscopic analysis) and micrographic inspection to ensure freedom from cracks and control of inclusions.
• Carburization/decarburization: Limits on total and partial decarburization; thickness of partial decarburization is controlled (inspection by microscopy or Vickers microhardness per referenced methods).
• Surface discontinuities: Permissible types and maximum depths are defined (normative Annex A); cracks are prohibited. Magnetoscopic or penetrant inspection methods are referenced.
• Thread and dimensional control: MJ thread limits and related dimensions are to be met; the standard complements dimensional limits in ISO 5855‑2.
• Mechanical and functional characteristics: Definitions and requirements for self‑locking torque, seating/unseating torque, breakaway torque, and wrench torque are provided to ensure functional performance.
• Quality assurance and inspection:
  • Manufacturer approval and quality system per ISO 9002.
  • Qualification tests performed on each type/diameter - typically 100 nuts sampled from a single batch.
  • Production acceptance inspections on each batch using sampling plans (AQL concepts from ISO 2859‑1).
  • Option to use Statistical Process Control (SPC) in lieu of final sampling when validated and approved.
• Sampling and test methods: References numerous normative documents for specific test procedures (e.g., ISO 3452 for penetrant inspection, ISO 3887 for decarburization measurements).

Applications

• Procurement and acceptance of high‑temperature aerospace fasteners for airframe, engine accessory, and other critical assemblies.
• Use in specification clauses on purchase orders, qualification dossiers, supplier approvals and quality control plans.
• Basis for supplier audits, lot release, and functional testing of self‑locking nuts rated up to 425 °C.

Who uses this standard

• Aerospace fastener manufacturers and suppliers
• Procurement and quality engineers in aircraft and space companies
• Certification authorities and prime contractors
• Design engineers specifying high‑temperature nuts in aerospace hardware

Related standards

Relevant referenced documents include ISO 5855‑2 (MJ threads), ISO 7481 (test methods for self‑locking nuts to 425 °C), ISO 2859‑1 (sampling/AQL), ISO 3452 (penetrant inspection), ISO 3887 (decarburization) and ISO 9002 (quality systems). These should be consulted for specific test procedures and dimensional limits.