ISO 9140:1998

Overview

ISO 9140:1998 defines standardized test methods for metric plain or slotted (castellated) aerospace nuts with MJ threads in accordance with ISO 5855-2. The standard describes the test devices and step‑by‑step procedures to verify mechanical and dimensional performance for nuts used in aerospace construction. It is intended to be referenced by product standards, procurement specifications and used in conjunction with ISO 9139 (supply specification).

Key topics and technical requirements

• Scope and applicability
  • Applies to metric plain or slotted (castellated) nuts with MJ threads for aerospace when referenced by product or procurement documents.
  • Tests are to be performed at ambient temperature.
• Hardness testing
  • Accepted methods: Rockwell (ISO 6508), Vickers HV5–HV100 (ISO 6507‑1), superficial Rockwell (ISO 1024) and microhardness.
  • Measurements taken on bearing face or nut flat; if impossible, sectioned and mounted in thermosetting resin.
  • Surface coatings or lubricants must be removed; tested nuts are not reused.
• Perpendicularity of bearing face
  • Uses a threaded mandrel (per ISO 5855‑2 flank diameter adjustments), a sliding ring (outer diameter ≥ nut flat size) and a shim whose thickness equals the allowable perpendicularity deviation in the product specification.
  • Nut is threaded fully onto the mandrel, ring applied and shim used to evaluate deviation.
• Axial load (proof) test
  • Test fixture includes a hardened backing plate (>40 HRC) and a test bolt per ISO 5855‑2 with tensile strength greater than the nut.
  • Two procedures: 80% load and 100% load (values taken from procurement specification). Apply load slowly, then unload; inspect visually and, if required, metallographically (×10).
  • Tested nuts must not be reused.
• Brittleness/fragility under stress
  • Applicable when nut hardness >39 HRC (unless otherwise specified).
  • Uses a hardened block (>40 HRC), cadmium‑plated (or equivalent) bolt, and washer. Nut torqued to specified torque using a closed socket/wrench per ISO 691 and held under axial tension for the specified time, then inspected.

Applications and users

• Who uses it:
  • Aerospace fastener manufacturers, quality control and inspection labs, OEM procurement/specification engineers, certification bodies, and design authorities.
• Why it matters:
  • Ensures repeatable, auditable tests for mechanical integrity and dimensional conformity of nuts used in critical aerospace joints.
  • Helps procurement and design documents cite consistent test methods and acceptance criteria for safety‑critical fastening components.

Related standards

• ISO 5855‑2 (MJ thread dimensions)
• ISO 9139 (supply specification for nuts)
• ISO 6507‑1 (Vickers hardness)
• ISO 6508 (Rockwell hardness)
• ISO 1024 (superficial Rockwell)
• ISO 691 (socket/wrench opening tolerances)

Keywords: ISO 9140:1998, aerospace nuts, castellated nuts, MJ threads, test methods, hardness test, axial load test, perpendicularity test, fragility test, fastener testing.