Which screw should I use for sheet metal?
Which screw should I use for sheet metal?
A self-drilling (Tek) screw with a drill point matched to the material thickness, or a self-tapping screw into a correctly sized pilot hole.
A thread cut in sheet metal has very little engagement — in 1 mm steel a screw has one thread of grip — so almost all the strength comes from the sheet, not the screw. That is why thin material calls for rivets or rivnuts rather than more screws, and why over-torquing strips a self-tapper instantly and permanently. Self-drilling screws are specified by point size for a thickness range, and using one outside its range is the usual cause of a screw that spins without penetrating: the point work-hardens the sheet, and once the surface is glazed, nothing will start. Coatings matter outdoors, since a screw that breaches a galvanised sheet becomes a galvanic couple and rusts around the hole.
The options, ranked
| Option | Good at | Bad at |
|---|---|---|
| Self-drilling (Tek) screw | Drills, taps and fastens in one action, which is why steel framing goes up so quickly. | The drill point is sized for a thickness range; too thin and it strips, too thick and the point wears out before it penetrates. |
| Self-tapping screw into a pilot hole | Precise and reliable, and the right approach in thicker or harder material. | Needs the correct pilot size — too small strips the screw, too large strips the thread. |
| Rivet | Vibration-proof and flush, and the aviation and bodywork standard for thin sheet. | Permanent, and it needs access to both sides for some types. |
| Machine screw with a nut or rivnut | Repeatedly demountable and much stronger in thin material than any thread cut in the sheet itself. | Needs access behind, or a rivnut tool. |
Technique that changes the outcome
- Match the drill point size to the sheet thickness
- Use steady pressure and low speed so the point can cut rather than skate
- Clamp the sheets together first; a gap means the screw drills the second sheet away from the first
- Deburr and, outdoors, seal around the head
What goes wrong
- Over-torquing, which strips the thread in one turn
- Using a self-drilling screw outside its thickness range
- Plain steel screws in galvanised or aluminium sheet, which corrode galvanically
Compiled practical guidance rather than a published standard. Product formulations vary by brand and market, so read the label — and where the work is structural, electrical or gas, the regulations that apply where you are govern rather than anything here.
Other screw questions
| For | Use |
|---|---|
| Wood | A pilot hole matching the screw's core diameter in the lower piece and a clearance hole in the upper one — that is what makes a joint tight. |
| Decking | Stainless steel — 304 inland, 316 near the coast — or a screw specifically rated for modern treated timber, which eats ordinary zinc plating. |
| Masonry | A concrete screw into a precisely sized hole, or a plug and screw — and hollow block needs a different anchor entirely. |
| Plasterboard | Coarse-thread bugle-head drywall screws into timber studs, fine-thread into metal studs — and never use them for anything structural. |
| MDF | A straight-shank MDF screw with a parallel thread, always into a pilot hole — the edge splits without one. |
| Chipboard | A twin-thread chipboard screw with an unthreaded shank under the head, so it pulls the joint together instead of bursting the board. |
| Plastic | A thread-forming screw designed for plastic, or a heat-set threaded insert where the joint will be undone more than once. |
| Roofing sheets | A hex-head screw with a bonded EPDM washer, driven until the washer just spreads — no further. |
| Brass hardware | Cut the thread with a steel screw of the same size first, wax the brass one, and use a driver that fits the slot exactly. |
Common questions
- Which screw should I use for sheet metal?
- A self-drilling (Tek) screw with a drill point matched to the material thickness, or a self-tapping screw into a correctly sized pilot hole.
- What should I avoid?
- Over-torquing, which strips the thread in one turn Using a self-drilling screw outside its thickness range Plain steel screws in galvanised or aluminium sheet, which corrode galvanically
Related pages
- Which screw and pilot hole should I use for wood? A pilot hole matching the screw's core diameter in the lower piece and a clearance hole in the upper one — that is what makes a joint tight.
- Which screw should I use for decking? Stainless steel — 304 inland, 316 near the coast — or a screw specifically rated for modern treated timber, which eats ordinary zinc plating.
- Which screw should I use in masonry? A concrete screw into a precisely sized hole, or a plug and screw — and hollow block needs a different anchor entirely.
- Which screw should I use for plasterboard? Coarse-thread bugle-head drywall screws into timber studs, fine-thread into metal studs — and never use them for anything structural.
- Which screw should I use in MDF? A straight-shank MDF screw with a parallel thread, always into a pilot hole — the edge splits without one.
- Which screw should I use in chipboard? A twin-thread chipboard screw with an unthreaded shank under the head, so it pulls the joint together instead of bursting the board.
- Which screw should I use in plastic? A thread-forming screw designed for plastic, or a heat-set threaded insert where the joint will be undone more than once.
- Which screw should I use for roofing sheets? A hex-head screw with a bonded EPDM washer, driven until the washer just spreads — no further.
- How do I drive brass screws without snapping them? Cut the thread with a steel screw of the same size first, wax the brass one, and use a driver that fits the slot exactly.
Sources
- Typical range compiled from manufacturer specifications — At One Place