ISO 4161:2012

Overview

ISO 4161:2012 specifies the characteristics of hexagon nuts with flange, style 2 - coarse thread. It applies to metric coarse threads from M5 to M20 inclusive, and defines product grades: A for threads up to and including M16 and B for threads above M16. The standard covers dimensions, tolerances, mechanical properties references and gauging methods to ensure interchangeability and consistent quality for flange hex nuts.

Key topics and requirements

• Scope and designation
  • Applies to hexagon nuts with flange (style 2), coarse threads M5–M20.
  • Example designation: “Hexagon nut with flange ISO 4161 - M12 - 10”.
• Dimensions and geometry
  • Detailed nominal sizes, pitches and dimensional limits (height, flange thickness, width across flats/corners) are given in Figure 1 and Table 1.
  • Corner radii and edge contour guidance are included; certain sizes (e.g., M14) are noted as preferably avoided.
• Thread and tolerance
  • General-purpose metric thread standards and tolerance class 6H are referenced.
  • Thread tolerances and limits are to follow ISO 261 / ISO 965-2 where applicable.
• Product grades and mechanical properties
  • Product grade A for D ≤ M16 and B for D > M16 (per ISO 4759-1).
  • Mechanical property classes (e.g., 8, 9, 10, 12) and stainless grades (e.g., A2-70) are specified by reference to ISO 898-2 and ISO 3506-2.
• Gauging and acceptance
  • Annex A gives a recommended gauging method using two plain ring gauges (A and B) and a feeler or ring gauge (C) to check hexagon height, flange thickness, corner fill and width across corners.
  • Acceptance inspection references ISO 3269; surface discontinuities per ISO 6157-2.
• Finishes and coatings
  • Electroplating per ISO 4042, zinc flake per ISO 10683, and hot-dip galvanizing per ISO 10684. Additional finishes to be agreed between purchaser and supplier.

Applications and users

ISO 4161:2012 is intended for:

• Fastener manufacturers producing hexagon nuts with flange (style 2) to ensure dimensional conformity.
• Design and mechanical engineers specifying reliable, interchangeable flange hex nuts in assemblies.
• Quality inspectors and procurement teams performing gauging, acceptance and supplier audits.
• Supply chain and standards compliance professionals ensuring parts match international mechanical and coating requirements.

Typical applications include machinery assemblies, automotive components, construction connections and any bolted joint requiring integrated flange nuts for load distribution and assembly reliability.

Related standards

Key referenced standards for threads, tolerances, properties and testing:

• ISO 225, ISO 261, ISO 724, ISO 965-2
• ISO 898-2, ISO 3506-2 (mechanical properties)
• ISO 4759-1 (product grades)
• ISO 3269 (acceptance inspection), ISO 6157-2 (surface discontinuities)
• ISO 4042, ISO 10683, ISO 10684 (coatings)

Keywords: ISO 4161:2012, hexagon nuts with flange, style 2, coarse thread, M5–M20, product grade A, product grade B, gauging, fastener standards.