A screw is fitted with only one bullet pad or only a flat pads, or two combinations with a single tooth. The combination screw state marking is expressed in GB9074. The common Cross Groove small pan head three combination screw state marking is GB9074.8. 8 of this is a small pan. That is, the head size of the pan-headed screw. The letter is expressed as PM. Professional combination screw manufacturer, habitual expression method is triad pm. The common cross groove cap combination screw state marking is GB9074.4. A combination screw that specializes in the head of the cap. or R-Head, or B-head. That is to say the head of the combination screw is larger than the head of the small pan and a thick dot. There is also a common type of hexagonal combination screw, which is a cross hexagonal combination screw. A hexagonal hexagonal combination screw is often called a concave hole. The national marking is GB9074.13.