The head of the carriage bolt is designed as a round shape without the design of a booster tool such as a cross slot or hexagonal socket, which serves as an anti-theft device during the actual connection process. In addition, the square neck of the carriage bolt can be stuck in the groove during the installation process, preventing the bolt from rotating and allowing it to move parallel in the groove. According to the size of the head, they can be categorized into large semi-circular head (corresponding to standards GB/T14 and DIN603) and small semi-circular head (corresponding to standards GB/T12-85). These bolts need to be used in conjunction with the nut, and do not connect individually. The tool is usually a wrench.