A Self–Drilling Screw is a Self-Tapping Screw with the added feature of a drill point. Generally this drill point looks a lot like the point of a drill. It will drill a hole and form the mating threads in one operation. If a screw will drill its own hole. A drill bit and sharp cutting threads that tap the hole during installation. Self drilling screws are a commonly used variety of screw for quick drilling into both metal and wood.
How it is measured: Whereas Flat head, countersunk screws are flat on the top of the head. They are measured from the top of the head to the tip. From that point to the tip is the length of the screw. Measured all the way to the end of the drill point tip.
Self–Drilling: Similar to the self–tapping, it has a drill shaped point which allows it to cut through thick and hard material without having to drill a pilot hole. Self-Piercing: Moreover screw has the ability to pierce the material at sharp angles. Between 25 to 30 degrees at high speeds. While thread-cutting screws are used when working with wood or metal – and one downside to using thread-cutting screws is that the threads could strip as the application is taken apart. This may prevent you reusing the fastener on a future project