A bolt with a seat under the head (or to omit a plain washer) is called a flange bolt. The forces required to secure the connection of the threaded and nut parts are the axial force that pulls the threaded part, the frictional force from the threaded and nut joints, and the friction proportional to the installation surface between the area under the head and the object. These forces are crucial for the bolted connection. Flange bolts come in various forms, including those that enhance frictional force by expanding the seating surface, those with added resilience by slightly rounding the flange, and those with serrations on the bottom seating surface, allowing them to tighten by biting into the material.