Self-tapping vs self-drilling screws: which to use

Tip two boxes of screws onto the bench and a self-tapping and a self-drilling screw look almost like twins. Pick the wrong one, though, and the job tells you soon enough - a screw spinning uselessly in a hole it can't grip, a stripped thread, or a sheared head where the metal was simply too much for it. It's a small choice that decides whether a fix takes ten seconds or ten minutes.

The difference lives right at the tip. A self-drilling screw has a little drill bit built into its point, so it bores its own hole and fixes in one go - brilliant in thin metal, no pilot hole, no swapping tools. A self-tapping screw cuts its own thread as it goes, but it usually needs a pilot hole to start in anything harder than plastic or thin sheet. Get that distinction straight and the rest is easy.

What a self-tapping screw does

A self-tapping screw forms or cuts its own mating thread as you drive it in, so you don't need to tap a thread separately first. There are really two flavours. Thread-forming screws push the material aside to make the thread, which suits softer materials like plastics and thin sheet where nothing is removed. Thread-cutting screws actually shave a thread, like a tap, which suits harder materials such as metal and leaves a cleaner, stronger hold. Either way, in anything more substantial than plastic or light sheet you'll drill a pilot hole first to give the screw a clean start and stop it wandering or splitting the material.

What a self-drilling screw does

A self-drilling screw - you'll also hear them called Tek screws - carries a fluted drill point that bores the hole as the screw advances, then taps its own thread straight after. It's a genuine one-shot fix: no pilot hole, no changing from drill to driver, just drive it home. That makes them a favourite for fixing thin steel and sheet metal at speed, roofing, cladding, ducting and steel framing among them. The catch is that the drill point is sized for a certain thickness of metal; go beyond what the point can clear and it will struggle or fail, which is where a pilot hole and a self-tapping screw take over.

Side by side

So which should you reach for?

If you're fixing into thin or medium steel and want speed - especially the same repetitive fix, over and over - a self-drilling screw earns its keep by cutting a step out of every fixing. If you're working across a mix of materials, into plastic or wood, or into metal thicker than a drill point can handle, a self-tapping screw with the right pilot hole gives you more control and a wider working range. Plenty of workshops keep both to hand and simply match the screw to what's in front of them.

Whichever you choose, the head and drive matter too - pick a head that sits the way you need (countersunk to sit flush, pan or hex for clamping force) and a drive that won't cam out under load. If you're buying for a workshop or a production line, it pays to standardise, so ask us for a quote on the sizes and finishes you use most.

Getting a clean fix

A few habits make the difference between a fixing that holds for years and one that works loose. For self-tapping screws, size the pilot hole to the screw's core (shank) diameter, not its outside thread - too big and there's nothing for the thread to bite, too small and you risk splitting the material or snapping the screw. For self-drilling screws, make sure the drill point is rated for the metal thickness you're going into, and let the point do its work before the thread engages rather than leaning on it. In both cases, drive at a steady speed and stop as soon as the head seats - overdriving strips the freshly formed thread and undoes all the holding power you just created. The right driver bit, matched to the screw's drive, saves a lot of chewed heads.

The short version

Self-drilling for speed in thin steel, no pilot needed; self-tapping for range and control across plastic, wood and thicker metal, usually with a pilot hole. Match the point to the material, size the pilot properly, and don't overdrive - do that and either screw will hold exactly as it should.

Browse our full range of screws and bolts, including self-tapping and self-drilling lines, or request a quote for the quantities you get through.

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Frequently asked questions

Do self-tapping screws need a pilot hole?

In plastic and thin sheet, usually not - the screw forms its own thread as it goes. In wood, and especially in thicker metal, drill a pilot hole first: it gives the screw a clean start, stops it wandering or splitting the material, and reduces the chance of snapping the screw. Size the pilot to the screw's core diameter, not its outside thread.

What are Tek screws?

"Tek" is a widely used name for self-drilling screws - the ones with a small drill point built into the tip. They bore their own hole and cut their own thread in a single action, which is why they're popular for fixing thin steel, cladding and roofing without pre-drilling.

Can a self-drilling screw go into thick steel?

Only up to the thickness its drill point is rated for. Each self-drilling screw has a point sized for a range of metal thickness; go beyond it and the point can't clear the hole and the screw will struggle or fail. For thicker steel, drill a pilot hole and use a self-tapping (thread-cutting) screw instead.

What's the difference between thread-forming and thread-cutting screws?

Both are types of self-tapping screw. Thread-forming screws push the material aside to create the thread, which suits softer materials like plastic where nothing is removed. Thread-cutting screws shave a thread like a tap, which suits harder materials such as metal and leaves a cleaner hold.

Which screw is best for sheet metal?

For thin to medium sheet metal, a self-drilling screw is usually quickest - it drills and fixes in one step with no pilot hole. If the metal is thicker than the drill point can handle, switch to a self-tapping screw with a correctly sized pilot hole.