The function of the Castle Nut is to fix the front and rear axle of the vehicle by fastening the screw through the front and rear wheel axles, so that the frame and the tire are fixed together. In order to prevent the nut from loosening, Must use split pin through the slot nut groove is fixed, the cotter pin to hold the slot nut must be through the middle shaft screw, shaft screw usually need to drilling, both the diameter of the hole and slot nut to the size of the slot width, and what size of split pin groove depth determines the selection, was elected with the shaft screw and split pin and slot nut are matching, nut through shaft screw to hold the front wheel and frame, split pin hole through the shaft screw fasteners, the slot nut, make the slot nut loose, do not produce the vehicle at the time of exercise is not loose.