When assembling carbon fiber parts and lightweight parts, screw retention and uniformity are critical, and the metric to measure these two elements is the torque at the time of assembly. Within the correct torque range, the part can be clamped without slippage or damage. Therefore, the torque wrench has become an indispensable tool for car dealers and professional car owners. What should we pay attention to when using it? Strictly speaking, a torque wrench is a type of measuring instrument. In particular, the mechanical preset torque wrench widely used in the industry is only used to determine the torque when tightening the screw, and must not be used as a special tool for dismantling to loosen the screw that has already been fixed. The preset torque wrench is usually used in one direction. When the screw is fixed clockwise and the preset torque is reached, the connecting rod is accelerated, and the instantaneous disconnection effect and warning sound are produced. Even if it can be converted to counterclockwise operation with the paddle of the ratchet, it can only be used to unscrew the screw that has already fallen off. After the meeting, the necessary torque for loosening the screw is much larger than the torque when tightening it (up to 1.5 times). Reverse use may cause the lever in the wrench to be stuck, causing it to be difficult to warn during forward use and unavoidable damage.