Overview
ISO 10684:2004 - Fasteners: Hot dip galvanized coatings specifies material, process, dimensional and selected performance requirements for hot dip spun galvanized coatings on coarse-threaded steel fasteners. The standard covers fasteners from M8 to M64 and property classes up to 10.9 for bolts/screws/studs and 12 for nuts. It focuses on spun hot-dip galvanizing of threaded items (and may be applied to other threaded or non-threaded steel parts such as washers), and it advises against galvanizing fasteners smaller than M8 or with thread pitches below 1.25 mm.
Key topics and technical requirements
- Scope & limits: Applies to coarse threads M8–M64; specifies behaviour for property classes up to 10.9 (bolts/screws/studs) and 12 (nuts).
- Materials & zinc: Raw material requirements referenced to ISO 898 series; zinc quality per ISO 1461.
- Galvanizing procedures:
- Cleaning, pickling and fluxing; inhibited acids recommended for hardened parts to limit hydrogen uptake.
- Stress relief and baking processes to avoid hydrogen embrittlement.
- Bath temperatures: normal galvanizing 455–480 °C; high-temperature process 530–560 °C (not used between 480–530 °C). High-temperature galvanizing is not recommended for property class 10.9 bolts/screws/studs M27 and above.
- Spinning and quenching immediately after removal from bath.
- Thread tolerances and assembly:
- Special thread tolerances and marking schemes to accommodate heavy zinc coatings (typically >40 µm).
- Two approved methods: nuts tapped oversize after coating (tolerance classes 6AZ/6AX, marked Z/X) or bolts/screws undersized before coating (6az, marked U). Never mate oversize nuts with undersized bolts.
- Guidance on allowable coating thickness relative to thread clearances.
- Coating requirements: appearance, minimum average/local thickness, adhesion and optional post-treatments (chromating/phosphating) to mitigate white rust.
- Testing & measurement: references to ISO measurement methods (e.g., ISO 1460, ISO 2064, ISO 2178).
Applications and who uses it
- Manufacturers of bolts, nuts, studs, screws and washers who hot-dip galvanize threaded parts.
- Galvanizing plants and quality control engineers implementing spun galvanizing processes.
- Design and procurement teams specifying corrosion protection for structural, construction, utility and industrial fastener assemblies.
- Inspectors and testing labs verifying coating thickness, adhesion and mechanical compatibility after galvanizing.
Practical value: ensures reliable thread fit, mechanical performance and corrosion protection for heavy zinc coatings on fasteners used in outdoor, marine and industrial environments.
Related standards
Keywords: ISO 10684:2004, hot dip galvanized coatings, fasteners, spun hot dip galvanizing, M8–M64, thread tolerances, nuts tapped oversize, coating thickness.
