Thread-forming screws may have a non-circular plan view, such as the five-fold symmetry of the pentalobular or three-fold symmetry for Taptite screws. Self-tapping screws can be divided into two classes those that displace material (especially plastic and thin metal sheets) without removing it are termed thread-forming self-tapping screws self-tappers with sharp cutting surfaces that remove the material as they are inserted are termed thread-cutting.
The lack of a sharp tip is helpful for packaging and handling and in some applications may be helpful for reducing the clearance necessary on the reverse of a fastened panel or for making more thread available on a given length screw.
The type B tip is blunt and intended for use with a pilot hole, often in sheet materials. Not all self-tapping screws have a sharp tip. Like the tip of a nail or gimlet, such a point forms the hole by displacement of the surrounding material rather than any chip-forming drilling/cutting/evacuating action. Thus, whereas a regular machine screw cannot tap its own hole in a metal substrate, a self-tapping one can (within reasonable limits of substrate hardness and depth).įor softer substrates such as wood or soft plastics, the self-tapping ability can come simply from a tip that tapers to a gimlet point (in which no flute is needed). įor hard substrates such as metal or hard plastics, the self-tapping ability is often created by cutting a gap in the continuity of the thread on the screw, generating a flute and cutting edge similar to those on a tap. Common features are the screw thread covering the whole length of the screw from tip to head and a pronounced thread hard enough for the intended substrate, often case-hardened. Self-tapping screws have a wide range of tip and thread patterns, and are available with almost any possible screw head design. Self-tapping screw with flute and type B (blunt) tip
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