Bolts, as one of the most widely used fasteners in mechanical engineering, are primarily used to connect two or more parts with holes through threaded connections. Their structure typically consists of a shank and a head, and they provide reliable connection and fastening functions in mechanical assemblies by applying torque to generate axial preload. Bolts are classified mainly according to their performance grade, head type, thread characteristics, and specific applications. Different types are suitable for various working conditions, ranging from general structural connections to applications involving heavy loads, impact vibrations, or corrosive environments.