Flange nut

Flange nut is a kind of nut with a wide flange at one end, which can be used as an integral washer. This is used to distribute the pressure of the nut over the fixed part, thus reducing the possibility of damage to the part and making it less likely to loosen due to uneven tightening surfaces. Most of these nuts are hexagonal and are made of hardened steel, usually zinc plated.
In many cases, the flange is fixed and rotates with the nut. The flange may be serrated to provide locking. The serrations are angled so that the nut does not rotate in the direction of loosening the nut. They cannot be used with gaskets or on scratched surfaces due to serrations. The serrations help to prevent the vibration of the nut from moving the fastener, thus maintaining the retention of the nut.
Flange nuts are sometimes equipped with rotating flanges to help form a more stable structure without affecting the finished product like serrated flange nuts. Rotating flange nuts are mainly used to connect wood and plastic. Sometimes both sides of the nut are serrated, allowing either side to lock.
The self-aligning nut has a convex spherical flange that mates with a concave dishwasher to allow the nut to tighten on a surface that is not perpendicular to the nut.