Expansion screws are used to drill holes with an impact drill and then fix objects to walls, ceilings, and floors with expansion screws. Expansion screws generally have an expansion sleeve, a screw with a tapered bottom, a nut, a flat washer, and an elastic washer.
A self tapping screw is a pointed screw used to fix objects on thin metal plates, such as color plates and aluminum alloy doors and windows. After drilling the bottom hole with a drill bit, do not tap it and screw it in directly with a self tapping screw.