Overview
ISO 9256:1993 specifies the configuration, dimensions and tolerances for large hexagonal‑head bolts used in aerospace applications. It covers bolts with a normal or pitch‑diameter shank and long‑length MJ threads, made of metallic material, coated or uncoated, and having strength classes ≤ 1 100 MPa. The standard is intended primarily for use when drawing up aerospace product standards and technical drawings.
Key topics and requirements
- Bolt geometry and configuration: Defines head form, shank type (normal or pitch diameter), thread type (long MJ threads) and optional hole/clearance features (figures for diameter codes 030–080).
- Dimensions and tolerances: All dimensions are expressed in millimetres. Table 1 in the standard gives diameter codes, length options and limit dimensions; unspecified form details are left to the manufacturer’s discretion.
- Surface condition and measurement basis: Dimensions apply after any surface coating but before application of lubricants.
- Edge treatment: Sharp edges are to be broken - the document notes a break of 0.1 to 0.4 mm where applicable.
- Length increments: The standard indicates increment rules for selecting greater lengths (see table notes - e.g., smaller and larger length step sizes are specified).
- Normative references: Relies on related standards such as ISO 286‑2 (limits and fits), ISO 3353:1992 (rolled threads - lead and runout), and ISO 5855‑2:1988 (MJ thread limit dimensions).
Applications and who uses it
ISO 9256 is used by:
- Aerospace engineers and designers specifying fasteners for airframes and equipment.
- Fastener manufacturers producing hexagonal head bolts to aerospace dimensional standards.
- Procurement and quality assurance teams verifying part interchangeability and conformity.
- Technical authors and standards teams drafting aerospace product standards, drawings and inspection plans.
Practical uses include preparing engineering drawings, defining procurement specifications, setting inspection criteria for dimensional compliance, and ensuring mechanical interchangeability across suppliers.
Related standards
- ISO 286‑2: system of limits and fits - tables of standard tolerance grades
- ISO 3353:1992: rolled threads - lead and runout requirements
- ISO 5855‑2:1988: MJ threads - limit dimensions for bolts and nuts
ISO keywords: ISO 9256, aerospace bolts, hexagonal head bolts, MJ threads, bolt dimensions, dimensional tolerances, aerospace fasteners, strength class ≤1100 MPa.