what's self tapping screw

Self-tapping screw is a kind of screw that can be tapped without drilling first. Self-tapping screws drill their own holes when they’re screwed into materials such as wood, plastic and metal. For hard substrates such as metal or hard plastic, self-tapping screws are created by cutting gaps in the continuity of the thread on the screw, creating a thread similar to the thread on the screw. So a normal screw can't tap its own hole in a metal substrate, but a self-tapping screw can (within reasonable limits of substrate hardness and depth). For softer substrates such as wood or soft plastics, self-tapping screw capability can simply occur from the tip tapering to the inner edge point (where grooves are not required). Similar to the tip of a nail or metal peg, such a point creates a hole by displacement of the surrounding material rather than any drilling/cutting/vacuuming action that creates chips.

Two self-tapping screws with different heads

This means that, in addition to the tap-like notch in the front thread, there is also a primary drill-like grooved end that looks very similar to the center drill on the end. Self-tapping screws combine drilling, tapping and installation actions; so they are very effective in a variety of hard substrate applications, from assembly lines to roofs.