What is the Difference Between a Self-Drilling Screw and a Self-Tapping Screw?
Self-tapping screws are one of the most commonly used industrial fasteners. As on of the earliest engineered fastener products, self-tapping screws were manufactured out of hardened steel, and their use powered the Industrial Revolution. Still incredibly common today, self-tapping screws now include many styles and types made for specific fastening functions.
Terminology used in the commercial fastener trade, unlike that used in aerospace or military fasteners, can be imprecise and often cause confusion. A prime example of this impreciseness is the distinction between self-tapping screws and self-drilling screws.
A self-tapping screw can accurately be described simply a tapping screw, but is also regularly referred to as a sheet metal screw, since they are used so heavily in the sheet metal trade.
Whichever name is used, a self-tapping screw (or sheet metal screw), is designated as such because it contains form mating threads (thereby “tapping” the threads) in a pre-drilled hole into which they are driven.
A self-drilling screw is a type of self-tapping screw that also features a drill point. The sharp drill point will both drill a hole and form the mating threads in a single operation.
So where does the confusion between terms come in? In many cases, the person specifying a this type of screw will interchange the terms self-tapping screw (or “Self-Tapper”) with self-drilling screw, but a screw is only a self-drilling screw when it will drill its own hole.
Other similar fasteners that could be considered to be self-tapping screws are:
Thread-Cutting Screws (TCS) - Screws that can be used to cut threads in a pre-drilled hole are known as thread-cutting screws. Thread-cutting screws are classified into different types depending on the thread-form to accomplish the thread cutting.
Thread Rolling Screws (TRS) - Screws that will roll or extrude threads in a pre-drilled hole in the substrate without removing any material are known as thread rolling screws. These screws create a very tight fit with zero clearance.
To recap, the terms self-tapping and self-drilling are not interchangeable. All self-drilling screws are self-tapping screws, but not all self-tapping screws are self-drilling screws. Both of these screws come in numerous configurations, and are widely used in the commercial, industrial and construction markets.
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