What size drill bit do I need for a wall plug?
Match the drill bit diameter to the plug diameter, not to the screw. Wall plugs are colour-coded by size and the pairing is standard:
- Yellow — 5mm plug, 5mm bit, screws roughly 3–4mm (gauge 4–6)
- Red — 6mm plug, 6mm bit, screws roughly 3.5–4.5mm (gauge 6–8)
- Brown — 7mm plug, 7mm bit, screws roughly 4.5–5.5mm (gauge 8–10)
- Blue — 10mm plug, 10mm bit, screws roughly 5.5–7mm (gauge 10–14)
Red and brown cover most household jobs.
The screw must be long enough to pass through whatever you are fixing plus the full length of the plug, and ideally slightly beyond it. A screw that stops short of the plug's end only expands part of it and the fixing pulls out.
Drill straight and to the right depth. A hole angled off square lets the plug sit proud. Drill slightly deeper than the plug so dust at the bottom does not stop it seating flush — wrapping tape round the bit gives you a depth marker.
Match the drill mode to the wall. Masonry and brick need a masonry bit and hammer action. Concrete lintels need an SDS drill for anything but the smallest holes. Never use hammer action on tiles — it cracks them; drill through tile on rotary only, with a tile or diamond bit, then switch to hammer once you are into the substrate behind.
Plasterboard is a different problem entirely. Ordinary plugs do not work in it — they spin in the hole. Use self-drive plasterboard fixings for light loads, or metal spring toggles for anything heavy. For a genuinely heavy load, find the stud and fix into timber.