Countersunk screws, also known as grub screws, grub screws, have a 90 degree cone on the head. Similar to ordinary wood screws, the head has tools for tightening grooves, shapes, crosses, hexagons, and the like. Countersunk screws are often used where the surface of the part cannot be raised after installation. The parts to be fixed are both thick and thin. The so-called thick, that is, the thickness of the part to be fastened is larger than the head of the countersunk screw. Thickness, after tightening the screw, part of the thread does not enter the threaded hole. In this case, the countersunk screws must be tightened.