ISO 4161 is the global reference standard for Hexagon Nuts with Flange featuring metric coarse threads. This international standard specifies the characteristics of flange nuts designed to provide a large bearing surface, effectively eliminating the need for separate washers in critical structural and mechanical assemblies.

Unlike many regional standards, ISO 4161 focuses on optimized dimensions for automated assembly and consistent load distribution. It is the primary choice for modern engineering projects requiring high-performance fastening with a focus on reducing assembly time and component count.

The technical focus of ISO 4161 is contact pressure management. The integrated flange distributes the clamping load over a wider area, reducing the surface pressure on the clamped parts. This is vital when fastening onto softer materials or across clearance holes. The standard ensures precise control over the nut height ($m$) and flange diameter ($d_c$) to guarantee compatibility with high-strength bolts.