Flange Nut (Serrated & Smooth)
Direct Answer
The Flange Nut (standardized under DIN 6923 and ISO 4161) is a hexagonal nut featuring an integrated wide, circular washer-like flange base. Available in smooth and serrated locking variants, it distributes clamping pressure over a larger surface area and eliminates the need for separate flat washers in high-speed automotive and industrial assembly.
Source: DIN 6923 / ISO 4161 / ASME B18.16.4
Specs
| Standard Specifications | DIN 6923 / ISO 4161 / ASME B18.16.4 |
| Flange Diameter Ratio | Flange Base Diameter $\approx 2.0\times$ to $2.2\times$ Thread Diameter |
| Bearing Surface Variants | Smooth Flange (load spreading) or Serrated Flange (mechanical anti-backoff teeth) |
| Serration Angle | Angled teeth that allow clockwise tightening but bite into metal during counter-clockwise loosening |
| Property Classes | Class 8, Class 10 (ISO 898-2) / Grade 5, Grade 8 (Imperial) |
| Primary Applications | Automotive exhaust and chassis, bicycle axle nuts, solar panel racking, sheet metal framing |
Serrated Flange Anti-Backoff Mechanics
Serrated flange nuts feature directional saw-tooth ridges on the underside of the flange. As the nut is tightened, the teeth slide smoothly over the metal surface. When vibration attempts to back the nut off, the steep edge of the serrations bites into the mating metal, requiring up to 10% more torque to loosen than to tighten.
Assembly Line Efficiency
By combining a hex nut and a flat washer into a single unified piece, flange nuts cut assembly handling time in half, prevent workers from dropping separate washers inside machinery, and span oversized or slotted mounting holes cleanly.