Overview
EN ISO 21670:2014 (ISO 21670:2014) covers specifications for hexagon weld nuts with flange (weld nuts) of product grade A. It defines sizes, material limits, mechanical properties, tolerances, marking and inspection rules for weld nuts intended to be welded to components and used with bolts up to property class 10.9 (per ISO 898‑1). Typical thread sizes covered are M5 to M16 (coarse) and fine-pitch variants (D = 8 mm to 16 mm).
Key topics and technical requirements
- Dimensions and connecting details: Nut geometry, flange and pressing contours, and recommended hole/plate thickness ranges are specified (see figures/tables in the standard).
- Threads and tolerances: Threads follow ISO 724 with tolerance class 6G (ISO 965‑3). Product grade: A (ISO 4759‑1).
- Material: Steel with a maximum carbon content of 0.25% and a maximum carbon equivalent (CEV) of 0.53% (CEV formula provided in the standard). Use of free‑cutting steels is prohibited. If quenched & tempered, hardness must not exceed 300 HV.
- Mechanical properties / proof loads: Proof load values are specified per size (tested in accordance with ISO 898‑2). Welding projections should be removed before testing in disputes.
- Surface finish & integrity: Nuts are delivered uncoated; manufacturers must ensure corrosion protection that does not impair weldability. Surface discontinuity limits are per ISO 6157‑2.
- Acceptance inspection: Procedures follow ISO 3269.
- Designation & marking: Standardized designation format (e.g., Weld nut ISO 21670 - M10 – St) and mandatory manufacturer mark on the face opposite the flange for sizes M5 and larger.
Applications and who uses this standard
- Designed for manufacturers and suppliers of fasteners, specifically hexagon weld nuts with flange used in welded assemblies.
- Relevant to industries that require welded nut attachments: automotive, heavy machinery, construction, metal fabrication and sheet‑metal assembly.
- Useful to:
- Design and mechanical engineers selecting weldable fastening solutions
- Purchasing/procurement teams specifying compliant components
- Quality/inspection personnel verifying acceptance criteria and proof load testing
- Standards managers and product developers ensuring weldability and mechanical compatibility with bolts up to class 10.9
Related standards
Normative references in EN ISO 21670:2014 include:
Keywords: hexagon weld nuts with flange, EN ISO 21670:2014, ISO 21670, weld nuts, fasteners standard, product grade A, M5 to M16, bolt property class 10.9, proof load, tolerances 6G.
