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.
Self-tapping screws have various names. They’re often called metal screws, sheet metal screws, tapping screws, or tapper screws.
Their tips come in different shapes: pointed (like a pencil), blunt, or flat, and they are described as thread-forming, thread-cutting, or thread rolling. If the screw is pointed, it will be thread-cutting – tapping and creating threads in a pre-drilled hole. If the tip is flat, it is thread-rolling – rolling or extruding threads and creating zero clearance between screw and material.
The most important difference between self-tapping and self-drilling screws is that self-tapping screws cannot go through metal without a pilot hole, which must be pre-drilled or pre-punched.
Exact drill or punch hole size is also important. The screw will become loose and not thread properly and securely if the hole’s too big. If the hole’s too small, the screw can break or cause the material to split or crack.
Self-tapping screws are good for use with metals, various types of plastics (plywood, fiberglass, polycarbonates), and cast or forged material, like iron, aluminum, brass or bronze. Self-tapping screws also work for surfaces where you can’t secure the rear end with a nut. Common applications include fastening aluminum sections, attaching metal brackets onto wood, or inserting screws into plastic housings.
Self-drilling screws are easy to distinguish if you look at their point, which curves gently at the end and is shaped like a twist drill. They’re often called Tek Screws, after the brand name that popularized them.
Screw lengths vary, but drill points are standardized, identifiable by number (1 to 5), which determines their length and thickness. Head and drive styles vary; self-drilling screws are most commonly Phillips, hex, or square.
Unlike self-tapping screws, self-drilling screws need no pilot hole to cut and fasten; they can drill, tap, and fasten in one go, which saves you the extra step of drilling, then fastening.
These screws can fasten metal to metal, wood to metal, and work well with light, low-density materials. In general, they have more specialized applications than self-tapping screws. They are good for metal building and light gauge metal assemblies; Point #5 is already capable of fastening half-inch steel sheets.
Self-drilling screws are useful in HVAC applications, cladding, metal roofing, steel framing, and other general construction tasks.
Self Drilling Vs Self Tapping: Which Is Better?
In the world of fasteners, the usual answer for which is better comes down almost entirely to the situation the fastener is being used for. From a time saving point of view, a self drilling screw is the better choice because it can eliminate the need for a drill bit making installations a one step process. However, both have their place and it comes down to knowing which to use in the situation at hand.