Self-drilling Screws

Self-Drilling screws (SDS) have a drill-shaped point to cut through sheet metal or steel which eliminates the need for drilling a pilot hole. These self-drilling screws are designed for use in soft steel or other metals.Self-drilling screw points are numbered from 1 through 5, the larger the number, the thicker metal it can go through without a pilot hole. A 5 point can drill a 0.5 in (13 mm) of steel.
Self-Tapping screws (STS) can cut their own threads as the screw is driven in to the material. They function by having a cutting edge which drills away the material, making a tiny hole for the screw to go into. This has nothing to do with the point of the screw but has everything to do with the threads which are designed to cut through the material.