Bolts are used to fix the internal parts of the engine, such as cylinder heads and cylinder blocks, to ensure that the engine components do not loosen or fall off during operation. Bolts are also used to connect various parts of the vehicle body, such as doors and roofs, to ensure the integrity and safety of the vehicle body structure. Although the nut is small, its function cannot be ignored. A loose bolt may cause serious safety problems. Therefore, it is of vital importance to regularly inspect and maintain the tightness of the bolts.