Overview
ISO 3225:1998 specifies the dimensional requirements for aerospace self-locking, fixed, two-lug anchor nuts (reduced series) with counterbore and MJ threads, for three high-temperature classifications: 1 100 MPa (ambient)/235 °C, 1 100 MPa (ambient)/315 °C and 1 100 MPa (ambient)/425 °C. The standard is intended to support the compilation of aerospace product standards and to ensure parts produced by different manufacturers are interchangeable.
Key normative points from the document include:
- Dimensions and tolerances are expressed in millimetres.
- Values given for surface texture and form tolerances apply before surface coatings and before lubricant application.
- The optional metallic cap, if used, shall remain attached to the nut at maximum operating temperature; test conditions are referenced to ISO 5858.
- Tolerances of form and position conform to ISO 8788.
Key Topics
- Scope and purpose: Defines dimensions for reduced-series, two-lug anchor nuts with MJ threads for specified high-temperature classifications. Applicable specifically for aerospace product standards compilation.
- Dimensional data: Includes figures and tabulated dimensions (see standard figures and tables) with notes on measurement points and permitted tooling marks.
- Surface and coating considerations: Dimensions apply after surface coating(s) but before lubricant; micrometre values for surface texture apply before coating.
- Attachment and performance: Metallic cap retention at elevated temperature is covered; the standard refers to ISO 5858 for performance/test criteria.
Applications
This standard is valuable for:
- Aerospace manufacturers producing anchor nuts to ensure dimensional interchangeability across suppliers.
- Procurement and quality teams specifying fasteners in aerospace product standards and procurement documents.
- Design and engineering groups selecting MJ-threaded two-lug anchor nuts where high-temperature performance and standardized sizing are required.
- Standards writers compiling or harmonizing aerospace fastener specifications with established thread and tolerance norms.
Practical benefits include consistent fit with mating bolts, reduced assembly risk, and streamlined procurement through standardized dimensions and referenced test methods.
Related Standards
- ISO 5855-2:1988 - Aerospace - MJ threads - Limit dimensions for bolts and nuts.
- ISO 5858:1991 - Aerospace - Self-locking nuts with maximum operating temperature ≤ 425 °C - Procurement specification (test conditions referenced).
- ISO 8788:1987 - Aerospace - Fasteners - Tolerances of form and position for nuts.
For full dimensional tables, figures and exact tolerances consult the official ISO 3225:1998 document. This summary highlights practical use, scope, and interlinked standards for engineers and procurement specialists working with aerospace fasteners.