Self Tapping Screws Self tapping screws are primarily designed to be screwed into sheet metal up to 1mm thick, but are also used in wood and plastic. The screws are mostly still manufactured in imperial gauge sizes No.2 to No.14 of various lengths. As the name suggests these screws form/cut threads in a pre-drilled hole in the receiving material ensuring a strong tightly fitted thread. As with any product designed to cut, these screws will only cut into material which is softer than the screw material. A full range of screw head and drive types are on offer to suit your application.