The one rule: the bit matches the plug
Get one thing right and wall plugs are easy: the drill bit matches the plug, and the screw is 1–2 mm smaller than the bit. A red plug wants a 6 mm hole and roughly a 4–5 mm (No.10) screw. Nearly every wall-plug failure comes from getting this backwards — an oversized hole the plug just spins in, or a screw so fat it splits the plug before it grips.
UK plugs are colour-coded so you can read the size off the plug: yellow 5 mm, red 6 mm, brown 7 mm, blue 8–10 mm, grey 10–12 mm. It’s a common convention, though — not a guaranteed standard — so it varies a little by brand. Always sanity-check against the packaging, which prints the bit and screw sizes.
Why your wall plug spins — and how to stop it
- Use the exact bit size — don’t oversize. The number-one failure is a hole that’s too big, so the plug turns instead of gripping. If the hole’s already too big, go up one plug size, or fill it and re-drill.
- Depth beats width. In brick with voids, go longer, not wider — extra width invites splitting, extra length adds holding strength.
- Drill slightly deeper than the plug, then clear the dust. Dust packed in the bottom of the hole stops the plug seating and causes pull-out — blow or vacuum it out before you push the plug in.
- Drill the brick, not the mortar. The brick or block holds far better than the softer mortar joint.
- Get past the plaster. A plug gripping only the soft plaster skim will pull straight out — drill through into the brick or block behind and seat the plug there.
When a wall plug is the wrong fixing
Never in plasterboard. A wall plug needs solid material to expand against; in hollow plasterboard it just spins and tears out. Hanging on a stud wall or ceiling? That’s a job for a drywall anchor, a different fixing entirely.
Above roughly 50 kg per fixing, step up from plastic. Grey plugs top out around 45 kg in good brick, and past that a plastic plug is the wrong tool — move to a steel sleeve anchor or another concrete anchor sized for the load. Think of it as picking the right fixing, not as fine print.
And whatever the plug, brick and block need the right kit to drill: a hammer drill and a carbide masonry bit. If you’re unsure which bit that is, the masonry drill bit guide covers it, and the drill bit size converter turns any millimetre size into the nearest bit you own.
Common questions
What size drill bit for a red wall plug?
A 6 mm drill bit. Red is the UK default wall plug (rawlplug): drill a 6 mm hole with a masonry bit, and use a screw around 3.5–5.0 mm (roughly a No.8–No.10). The rule is that the bit matches the plug and the screw is 1–2 mm smaller than the bit. Red holds about 20 kg in solid brick as an indicative maximum — check the packaging and, for anything that matters, the manufacturer's datasheet.
What size drill bit for a brown rawlplug?
A 7 mm drill bit. Brown plugs are the medium-heavy step up from red — drill 7 mm and use a screw around 4.0–6.0 mm. They suit curtain poles, shelving and kitchen units, holding roughly 25 kg in solid brick as an indicative figure. As always, the screw is a size smaller than the bit, and you should confirm against the plug's packaging.
What size screw for a red wall plug?
Around a 3.5–5.0 mm screw — roughly a No.8 to No.10 — for a red wall plug. The key point is that the screw is 1–2 mm SMALLER than the 6 mm drill bit, so it bites into the plug and expands it against the wall. Too fat a screw splits the plug; too thin and it never expands enough to grip. When in doubt, the plug's packaging lists the screw range.
Can you use wall plugs in plasterboard?
No. A wall plug needs solid material — brick, block or concrete — to expand against. In hollow plasterboard it has nothing to grip, so it just spins in the hole and pulls straight out under load. For a plasterboard (drywall) wall, use a proper drywall anchor instead — a self-drilling anchor, a spring toggle or a molly bolt — matched to the weight, or better still fix into a stud.
Why does my wall plug spin?
Almost always because the hole is too big. If you drilled oversize — or the bit wandered, or the plug is in soft mortar or plaster rather than brick — the plug turns instead of gripping the wall. Fixes: use the exact bit size for the colour (6 mm for red, 7 mm for brown, and so on), go up one plug size if the hole is already too large, or fill the hole and re-drill. Make sure you're drilling into the brick itself, past any plaster skim, and clear the dust before inserting the plug.
Where these numbers come from
The colour-to-size mapping here is cross-referenced across UK fixing suppliers and manufacturer references — including Rawlplug, Screwfix, Toolstation and several UK trade and DIY guides — which agree on the core sizes: yellow 5 mm, red 6 mm and brown 7 mm are unanimous, while blue (8–10 mm, commonly 10) and grey (10–12 mm) vary a little by brand. Load figures are indicative maxima in solid brick and genuinely differ between sources at the margins, so they’re given as approximate guidance, never as rated specifications. Colour coding is a widely-followed convention rather than a formal standard — the packaging is always the final word. For structural or safety-critical fixings, follow the manufacturer’s data and step up to an engineered anchor.
Wall-plug sizing here is common-convention UK guidance for light-to-medium DIY fixings. Colour coding and load figures vary by brand — always follow the plug packaging. Loads are indicative maxima in solid brick, not rated specifications; for structural, heavy or safety-critical fixings, step up to an engineered anchor and follow the manufacturer's data.