Despite their widespread availability and usage in commercial, industrial, and construction applications, many still confuse self-tapping screws with self-drilling screws.

Part of the reason this happens is that self-drilling screws are a subtype of self-tapping screws.

Let’s go through these two products separately to clarify these differences.

Self-Tapping 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

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.

Similarities and Differences

What’s most similar about these two types of screws is that both form threads as they penetrate the material being worked with. Both attach steel on steel and steel on wood when rivets or nuts and bolts cannot do the job.

Between these two, however, self-drilling screws offer two distinct advantages: time and costs saved at assembly time, and reduced error in installation, which often happens if one pre-drills holes in the wrong size.