If you're fixing to steel, the two terms you'll see everywhere are self-tapping and self-drilling — and they get used interchangeably on site, which is exactly how the wrong screws end up in the van. They're related but not the same, and picking the wrong one either wastes time drilling you didn't need, or stalls out entirely because the screw can't cut its own hole. Here's the difference and how to choose.
The one-line difference
- A self-tapping screw cuts its own thread into a pre-drilled pilot hole. It can't make the hole itself.
- A self-drilling screw (the type everyone calls a tek screw) has a drill point built into the tip, so it drills, taps and fixes in one operation — no pilot hole.
Both are "self-tapping" in the sense that they form their own thread. The drill point is the dividing line.
When a self-tapping screw is the right choice
Self-tappers (type AB / thread-cutting screws) shine when you already have a hole — either drilled by you or formed in a thinner material:
- Fixing into pre-drilled holes in sheet steel or plate.
- Thin sheet metal work, ducting, and enclosures where a 2.9–4.8mm screw is all you need.
- Wood-to-metal and general trade fixing where you control the pilot hole.
Our self-tapping screws range covers pan head, countersunk and flanged Type AB screws from 2.9mm to 4.8mm, in bright zinc plated and black finishes.
The catch: every job needs a pilot hole sized to the screw and the steel thickness. Too big and the thread won't bite; too small and you'll snap screws or burn out drivers. It's an extra operation on every fixing.
When a tek (self-drilling) screw wins
Tek screws carry a drill point that does the hole-making for you, which is why they dominate roofing, cladding and steel framing work:
- Sheet-to-steel fixing with no separate drilling pass.
- Wood-to-steel connections, including heavy sections — see our wood-to-heavy-section steel screws.
- Roofing and cladding, with bonded washers for weather sealing.
We stock a deep tek range — 19 subcategories from sheet-to-timber to heavy-section steel — all covered in what are tek screws? and the full drill-point breakdown in tek screw sizes and points explained.
Quick decision guide
| Your job | Reach for |
|---|---|
| Hole already drilled in steel plate | Self-tapping (Type AB) |
| Thin sheet, you want one-pass fixing | Self-drilling tek screw |
| Roofing/cladding into purlins or rails | Tek screw with bonded washer |
| Wood to heavy steel section | Wood-to-steel tek screw |
| Fine metalwork, small screws, controlled pilot holes | Self-tapping |
Two things that catch people out
- Point length vs steel thickness. A tek screw's drill point must fully penetrate the steel before the thread engages — if the point is too short for the section, the threads bind on the surface before the hole is through. Match the point to the material thickness (the tek sizes post has the chart).
- Self-tappers into thick steel. Type AB screws cut thread; they don't machine hole. Past thin sheet, you're better off drilling clearance and tapping properly, or stepping up to a tek with the right point.
Ordering from Fastco
Both ranges are live on site: self-tapping screws and self-drilling tek screws, with fast UK delivery and no account needed to order. Not sure which point type suits your steel thickness? speak to an expert on 01270 252 326 (Monday–Friday, 8:00am–4:30pm) or email [email protected].
FAQ
Are self-drilling screws the same as self-tapping?
All self-drilling screws are self-tapping, but not the reverse: a self-tapping screw needs a pre-drilled pilot hole, while a self-drilling (tek) screw drills its own hole first.
Can I use self-tapping screws on steel without drilling?
No — self-tapping screws cut their thread into an existing hole. For one-pass fixing into steel you need a self-drilling tek screw.
What size self-tapping screw for sheet metal?
Our range runs 2.9mm to 4.8mm in pan, countersunk and flange heads — pick the diameter to suit the hole and the head to suit the finish.
