Automatically adjusting arm increases the external adjustment mechanism of the brake gap. It can change the original brake gap at any time to correct the brake deviation and friction caused by the inconsistent friction area of the friction plate. This function is to make up for the defects of the brake. The self-adjusting arm is already a mature technology abroad and has been widely applied. The QT500-7 and QT600-3 material automatic adjustment arm casting products and machined products have strong dimensional consistency, small hardness difference, stable performance and long fatigue life. The products are widely used in truck, bus, and trailer brake systems.