A flange nut is a nut with a wide flange at one end that acts as an integral washer. This is used to distribute the pressure of the nut over the part being secured, thus reducing the possibility of part damage and making it less likely to loosen due to uneven tightening surfaces. These nuts, most of them hexagonal, are made of hardened steel and are usually zinc-plated. In many cases, the flange is fixed and turns with the nut. Flanges can be serrated to provide locking. Serrated at an Angle so that the nut does not rotate in the direction in which the nut is loosened. They cannot be used with gaskets or on scratched surfaces due to serrated teeth. Serrated teeth help prevent vibration of the nut from moving the fastener, thus maintaining the nut's holding force.