Tek screws, also called self-drilling screws, are self-tapping in the same way as a sheet metal screw, but it has a drill-shaped point to cut through the substrate to get rid of the need for drilling a pilot hole. Tek screws are made for use in soft steel or other metals. The points are numbered from 1 through 5, Self-drilling screws, also known as Tek screws, have drill bit tips which are numbered from #1 up to #5. the bigger the number, the thicker metal it can go through without a pilot hole. For example, a # 5 point can drill a 0.5 in (12.7 mm) of steel.
Contractors sometime question the quality of their tek screws when the fasteners break, when the reason for the screws snapping is that they are not being used in the application for which they were designed. Here is a simple reason for heads of tek screws sometimes snapping off or the shank twisting and breaking when drilled into steel too thick for the tek screw used.
Example: 12-24X7/8 Hex Washer Head Self Drilling Screws ( Tek Screw )
With a common tek screw, the front of the screw will be drilling in slower while the drill bit is drilling the pilot hole than when the threads of the tek screw catch the material being drilled. Once the threads catch, the fastener will turn as fast as the TPI. In other words, if the-fastener is 16tpi, the screw will go in a 16th of an inch each time it turns. The problem becomes, if it is a thick piece of metal, the threads will catch before the drill bit is done drilling through the metal. The result is that the front of the screw will be moving slower than the back of the fastener and the screw will break.
However, by having the drill bit of the screw longer up the shank of the fastener, and modifying the threads per inch to a finer thread (24 threads per inch) the front and the back of the fasteners will move at the same time and the screws won’t break.