Overview - ISO 3223:1998 (Aerospace anchor nuts, dimensions)
ISO 3223:1998 specifies the dimensional requirements for a family of aerospace anchor nuts: self-locking, fixed, two-lug nuts with a counterbore and MJ threads. The standard covers nuts classified as 1 100 MPa (ambient) with maximum operating temperatures of 235 °C, 315 °C and 425 °C. It is intended solely for use in the compilation of aerospace product standards and defines the geometry, tolerances and key configuration details needed to produce interchangeable parts.
Key topics and technical requirements
- Scope and classification: Dimensions for self-locking, fixed, two-lug anchor nuts with counterbore and MJ threads for three temperature/strength classifications (1100 MPa at ambient / 235 °C, 315 °C, 425 °C).
- Dimensions and tolerances: All sizes and tolerances are given in millimetres (see Figure 1 and Table 1 in the standard). Values apply after any surface coating(s) but before application of lubricant.
- Thread standard: Thread limit dimensions reference ISO 5855-2 for MJ threads.
- Form and position tolerances: Conformance with ISO 8788 is required for tolerances of form and position.
- Procurement linkage: Geometry is determined to satisfy the procurement specification ISO 5858 for self-locking nuts (maximum operating temperature ≤ 425 °C).
- Operational notes:
- The metallic cap (if used) shall remain attached at the maximum operating temperature (test conditions per ISO 5858).
- Definitions: “1100 MPa” refers to minimum tensile stress capability at ambient temperature; the listed temperatures are maximums the nut can tolerate without permanent degradation (surface treatment affects this).
Practical applications
- Use ISO 3223:1998 to define and verify the dimensional interchangeability of aerospace anchor nuts in aircraft and space vehicle assemblies.
- Applicable in:
- Fastener design and CAD modelling for aerospace structures
- Manufacturing and tooling for MJ-threaded anchor nuts
- Quality control, inspection, and acceptance testing of nuts before assembly
- Preparation of aerospace product standards, drawings and procurement documents
Who should use this standard
- Aerospace design and structural engineers
- Fastener manufacturers and toolmakers producing MJ-thread nuts
- Procurement/specification writers creating material and purchase documents
- Quality assurance, inspection and maintenance (MRO) teams
- Standards developers compiling aerospace product standards
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: Tolerances of form and position for nuts
Practical takeaway: ISO 3223:1998 provides the authoritative dimensional and tolerance baseline for MJ-threaded, two-lug, self-locking anchor nuts used in high-strength, high-temperature aerospace applications - essential for designers, manufacturers and standards authors ensuring interoperability and reliability.