A flange nut is a nut that has that has one side shaped with a wide, flat surface. The surface, or flange, functions like a washer by preventing the nut from embedding in the surface being fastened when it is screwed onto the end of a bolt. It also distributes the holding power of the nut evenly over its surface to provide more secure fastening. Flange nuts are useful for attaching wood and metal parts and are widely used in carpentry, auto repair and industry. They are available in a wide range of sizes and materials.