Self-drilling screw is a screw that can tap its own hole as it is driven into the material. For hard substrates such as metal or hard plastics, the self-drilling 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. Thus, whereas a regular machine screw cannot tap its own hole in a metal substrate, a self-drilling one can (within reasonable limits of substrate hardness and depth).