hex head self tapping screw with rubber washer

The head of a bolt is also an essential part of its structure. The head of a bolt is the part that is turned to tighten or loosen the bolt. There are several types of bolt heads available, including hex, square, and round heads. Each type of bolt head serves a specific purpose and may be chosen based on the application requirements. For example, hex heads are the most common and provide a larger surface area for applying torque, while round heads are used in applications where a smooth finish is desired.

...

The functionality of metal expansion nuts centers around the principle of mechanical expansion. Upon the application of torque, the screw or bolt is threaded into the nut, which, in turn, causes the nut to expand outward. This outward expansion presses the sides of the nut against the inner walls of the hole it occupies, creating a tight fit. The added friction and mechanical grip prevent the nut from loosening over time, even in dynamic conditions.


...