ISO 10644:2009

Overview

ISO 10644:2009 specifies requirements for metric screw and plain washer assemblies made of steel where the plain washer is captive (prevented from disassembly but free to rotate). It covers coarse thread sizes M2 to M12, flat seating heads, and screw property classes up to 10.9. The standard defines two washer hardness classes - 200 HV and 300 HV - and the permitted combinations of screw property class and washer hardness.

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Key topics and technical requirements

• Scope and geometry
  • Applies to metric assemblies with coarse threads M2–M12 and flat seating heads.
  • Washer dimensions follow ISO 10673; screws conform to respective product standards (e.g., ISO 4014, ISO 4017, ISO 4762).
  • Bolts/screws may have a reduced shank so the captive washer can rotate freely; provisions cover underhead radius and transition diameters to avoid interference.
• Mechanical and material requirements
  • Screw mechanical properties referenced to ISO 898-1 (testing with washer removed for referee purposes).
  • Washer hardness rules: for screws ≤ 8.8, washers may be 200 HV or 300 HV; for property classes 9.8 and 10.9, washers shall be 300 HV.
• Manufacturing methods (Annex A)
  • Method 1: assemble screw blank with washer, roll threads, then heat-treat.
  • Method 2: manufacture components separately, heat-treat, then roll threads in hardened condition.
• Coatings and surface treatments
  • Coatings referenced: ISO 4042 (electroplated), ISO 10683 (zinc flake), ISO 9717 (phosphate). Other coatings by agreement.
• Designation
  • Standardized designation format includes reference to ISO 10644, screw characteristics, screw and washer symbols, and washer hardness (examples provided in the standard).

Practical applications

• Used where a captive plain washer is required for assembly reliability, easier handling, or to prevent loss of components in production and maintenance.
• Common in automotive, machinery, electrical panels, consumer products and any application needing standardized fastener assemblies with controlled washer hardness for load distribution and bearing performance.
• Ensures consistent torque/clamp load behavior by controlling washer hardness, dimensions and compatibility with screw underhead geometry.

Who should use this standard

• Fastener manufacturers and assemblers
• Product designers and mechanical engineers
• Procurement and quality assurance teams
• Test laboratories and standards compliance officers

Related standards

• ISO 10673 (plain washers)
• ISO 898-1 (mechanical properties of fasteners)
• ISO 4014 / ISO 4017 / ISO 4762 / ISO 7045 (screw product standards)
• ISO 4042, ISO 10683, ISO 9717 (coatings)

This summary helps engineers and procurement professionals quickly understand ISO 10644:2009’s scope, requirements, and practical use for standardized captive screw-and-washer assemblies.