All three of these make their own threads — that’s why they all get called “self-tapping.” The real question is how they do it, and whether you drill a hole first. Get that right and the screw does the work for you.
Pushes the material aside to form threads instead of removing it — like the common Type A, AB, and B sheet-metal screws. Best in thinner sheet metal, plastic, and soft material, where there’s give. Strong hold because no material is lost, but in anything too thick or hard it’ll fight you or strip.
Needs a pilot hole sized to the screwHas a cutting edge or flute that carves a thread, like a tiny tap — Type 23, 25, and F are common. Made for thicker or harder metal and castings, where forming would build up stress and crack the part. Cutting relieves that stress, but the thread it leaves is a touch less strong than a formed one.
Needs a pilot hole — usually a bit larger than a forming screwHas a little drill point on the tip, so it bores its own hole and threads in one shot — no pre-drilling. Great for fastening steel and metal panels fast. The catch: the drill point is rated for a limited steel thickness (shown as a point number, roughly #1 to #5). Too thick and the point never breaks through before the threads hit — so it just spins, heats up, and burns out.
No pilot hole — but mind the thickness it can drillThin sheet, plastic, or soft metal? A thread-forming sheet-metal screw, pre-drilled. Thick or hard metal, or a casting you don’t want to crack? A thread-cutting screw, pre-drilled. Steel panel or framing and you’d rather skip the drill? A self-drilling TEK — just make sure its point can handle how thick your steel is.
The most common mistake is reaching for a self-driller on steel that’s too thick for its point. If the screw spins without pulling in, that’s usually what happened — step up to a longer drill point or pre-drill and use a thread-cutting screw instead.
For thread-forming and thread-cutting screws, the pilot hole size matters: too small and you’ll strip the screw or split the work; too big and the threads have nothing to grab. The right size depends on the screw and the material, so it’s worth drilling a test hole in scrap of the same stock before you commit — or tell us the screw and material and we’ll point you to the right drill.
Bring a sample or describe what you’re fastening into and how thick it is. We’ll sort the type, point, and pilot so the first one goes in clean.
