Self Drilling Screws vs. Self Tapping Screws
What's the difference between a self-drilling screw and a self-tapping screw?
This topic has confused myself in the past as well as our customers. We are going to make it clear here the difference between these two fasteners, and what applications they are best used for. First I will show you a comparison image, and then explain the merits of each type of screw.
Self Drilling Screws (aka TEK® Screws)
Tek® Screws are a brand name first of all, but self drilling describes it very well. These screws work as both a drill bit and a fastener. Self-drilling screws do not need a pilot hole because of the drill bit end. They work quite well at fastening thin pieces of metal together and were designed for exactly this reason. We have customers use these when doing frame work on their cars, or attaching sheet metal to a metal frame. Why drill a bunch of holes into a metal sheet wearing out a drill bit, when you can use these guys. They also have much variance in types and uses than tapping screws.
Self Tapping Screws
Self tapping screws tap their own thread, so they need a pilot hole slightly smaller than the screws diameter. The idea is, you drill a pilot hole into wood or another soft material. Then as you drive the tapping screw in, its threads will dig into the material keeping it secure. Self tapping screws are ideal for all sorts of materials, including wood, metal, and brick. For harder surfaces, self tapping screws might have little notches on the thread to help cut the thread, just like a tap. Not all tapping screws have a pointy tip, some will be blunt or flat.
Here's where the confusion comes from, a self tapping screw can also be self drilling. Basically a self drilling screw is a tapping screw that doesn't need a pilot hole. They both technically tap their own threads, all screw do this to varying degrees. But, the self drilling screws skip a step in the process. The way self-drilling screw are made make them ideal for metal. You can use them with wood they won't grip as well because the have wasted length with no thread. I hope we have cleared up all the confusion, just remember all self drilling screws are self tapping, but not all self tapping screws are self drilling.