Bolts are a type of fastener without a head, featuring threads on both ends. During assembly, one end must be threaded into a part with an internal threaded hole, while the other end passes through a part with a through hole. Then, a nut is tightened to securely connect the two parts into a single unit. This type of connection is known as a bolt connection and is also a removable type. It is mainly used when one of the connected parts is thick and requires a compact structure, or when frequent disassembly is needed and bolt connections are not suitable.