Overview
ISO 8991:1986 - Designation system for fasteners - defines a standardized system for naming and specifying fasteners in product standards. Published by ISO (Technical Committee ISO/TC 2, Fasteners) in 1986, the standard provides a clear, repeatable format to present key fastener characteristics (thread, size, length, material, property class, surface finish, etc.) so product standards, manufacturers, procurement teams, and engineers can unambiguously identify parts.
Key topics and requirements
ISO 8991 sets out the components and order of information to use when designating fasteners in product standards:
- Denomination (product name) - e.g., Hexagon head bolt, Hexagon nut, Tapping screw
- Reference to the appropriate ISO product standard - e.g., ISO 4014, ISO 4036, ISO 7049, ISO 8676, ISO 2338, ISO 7090, ISO 4632
- Thread size or nominal size (e.g., M12, ST3.5)
- Further diameters or features (tolerance of pin diameter, pitch where applicable)
- Nominal length and thread length or shank length (where relevant)
- Type of product or variant (cone end type, recess type, pin type A, washer series)
- Property class, hardness, or material (e.g., 8.8, 10.9, 140 HV, St)
- Product grade, drive type, and surface protection (e.g., A2P electroplating, drive recess)
Examples given in the standard illustrate the format:
- Hexagon head bolt ISO 4014 - M12 x 80 - 8.8
- Hexagon nut ISO 4036 - M6 - St
- Tapping screw ISO 7049 - ST3,5 x 16 - C - Z
- Parallel pin ISO 2338 - 6m6 x 30 - A - St
The standard emphasizes that references to other ISO documents imply their latest edition unless otherwise stated.
Applications and who uses it
ISO 8991 is intended for use in:
- Writers of product standards who must present clear fastener designations
- Manufacturers and quality engineers documenting parts and production specifications
- Procurement teams and supply-chain specialists preparing purchase orders and bills of materials (BOMs)
- Designers and maintenance personnel who need unambiguous part identification for assembly, repair, and replacement
Using ISO 8991 enhances interoperability, reduces ambiguity in ordering and documentation, and supports consistent labeling across international markets.
Related standards
ISO 8991 is a framework used alongside specific product standards cited in examples, including (but not limited to):
Keywords: ISO 8991, fasteners designation, bolt screw nut designation, ISO fasteners, fastener marking, product standards.
