Even among contractors, who use screws everyday, there is often confusion as to why there are different numbers assigned to drill bit tips on tek screws. Self drilling screws,sometimes called tek screws, are self tapping in that they tap their own threads and don't need to be used with a pre-threaded insert. Unlike a regular sheet metal screw, they have a drill bit shaped point to cut through the substrate which does away with the necessity to pre-drill a pilot hole. Tek screws were designed for use in steel starting with 22 gauge and thicker . For anything lighter than 22 gauge, 24 gauge and thinner, a needlepoint, also known as a zip screw, will do the job! The points are numbered from 1 through 5 and the greater the number, the thicker metal it can go through without having to drill a pilot hole. For example, a # 5 point can drill a 0.5 in (12.7 mm) of steel.

The quality of a tek screw will frequently be questioned when they break when the actual reason is the application. With a self drilling screw, the drill bit on the front of the screw will drill in slowly while the bit is drilling the pilot hole and then, when the threads of the tek screw catch the metal, the back end of the screw will suddenly start going the the material faster than the drill bit can drill. Once the threads catch, the screw will turn as fast as the TPI, otherwise known an Threads Per Inch. In other words, if the fastener is 16tpi, the fastener will go in a 16th of an inch each time it turns. Where the problem arises is if the material 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 fastener will be moving slower than the back of the fastener and the fastener will break. However, by having the drill bit of the screw longer up the shank of the fastener, and altering the threads per inch to a finer thread (24 threads per inch) the front and back of the tek screws will turn at the same time and the shank of the fastener won't break in half .

Example: 12-24 x 1 1/4 Hex Washer Head Self Drilling Screws ( Tek Screw )

12 - (size of shank. Think dress size. bigger the number, thicker the shank)

24 - Number of Threads per Inch also known as TPI

1 1/4 - measurement from underneath the head to the tip of the screw.