Overview
ISO 3318:2016 specifies the maximum outside head dimensions for open-ended wrenches, box (ring) wrenches and combination wrenches used with screws and nuts. The standard defines dimensional limits for wrench heads and references schematic figures and a comprehensive table of values rather than prescribing a particular design. It is focused on dimensional compatibility and does not replace technical product specifications, which are given in ISO 1711-1.
This fifth edition updated the sizes covered in Table 1, extended scope to include single-headed wrenches, and removed the former Clause on technical specifications.
Key Topics
- Scope and purpose: Defines maximum outside head dimensions to ensure interchangeability and reduce interference during assembly.
- Dimensions and illustrations: Figures 1 and 2 (open-end and box end) accompany Table 1, which lists nominal widths across flats and corresponding maximum outside head dimensions.
- Tolerances: Dimensional tolerances are to be applied in accordance with ISO 691 (Wrench and socket openings - Tolerances for general use).
- Reference sizes: Table 1 covers a range of nominal widths across flats (s) and maximum outside head dimensions (b, c). Nominal widths shown in the standard include sizes from small to large tool sizes used in industry.
- Designation alignment: The wrenches covered are identified according to ISO 1703 nomenclature.
Applications
ISO 3318:2016 is practical for organizations that need consistent tool dimensions across design, manufacturing, and procurement processes. Typical uses include:
- Tool design and manufacturing: Ensure wrenches meet maximum head width limits to avoid interference in assemblies and tool storage.
- Procurement and specification writing: Provide clear dimensional constraints in purchase orders and supplier specifications.
- Quality control and inspection: Verify outside head dimensions against Table 1 and apply ISO 691 tolerances during inspection.
- Assembly line planning: Reduce tool–component conflicts where access or clearance is limited (tight engine bays, confined machinery, or dense component layouts).
Benefits include improved interchangeability, reduced assembly rework, and clearer supplier communication.
Related Standards
- ISO 691 - Tolerances for wrench and socket openings (normative reference for tolerances).
- ISO 1711-1 - Technical specifications for hand-operated wrenches and sockets (product specifications).
- ISO 1703:2005 - Designation and nomenclature of assembly tools for screws and nuts.
- ISO 272 - Hexagon product widths across flats (referenced where nominal widths overlap).
For implementation, consult the figures and Table 1 in ISO 3318:2016 and apply ISO 691 tolerances. Use ISO 1711-1 for complementary technical requirements when specifying or certifying tools.
Open preview (PDF)Assembly tools for screws and nuts — Open-ended wrenches, box wrenches and combination wrenches — Maximum widths of heads