ISO 10684:2004

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

• ISO 898-1 / ISO 898-2 (mechanical properties)
• ISO 965 series (metric thread tolerances)
• ISO 1460 / ISO 1461 (zinc coating determination and requirements)
• ISO 2064, ISO 2178, ISO 8991

Keywords: ISO 10684:2004, hot dip galvanized coatings, fasteners, spun hot dip galvanizing, M8–M64, thread tolerances, nuts tapped oversize, coating thickness.