Never use nylon wall plugs or plasterboard anchors for safety-critical fixings. Handrails, stair rails, banisters, balustrades, gates, ladders, climbing or play equipment, overhead fixings, and anything else whose failure could cause a fall or injury need a fixing designed and rated for that purpose — typically a through-bolt, a mechanical anchor or a resin-bonded anchor with a published load rating (and, for structural use, a European Technical Assessment). If you are not certain the wall and the fixing are up to the job, get advice from a builder or structural engineer.
This wall plug size chart covers the common UK plug sizes, the drill bit size for each and typical screw sizes. It does not give loads by colour, because a plug’s capacity depends on the product and the wall it goes into.
Bookmark this page — you’ll come back to it every time you pick up a drill.
Note: the plug and drill sizes follow Rawlplug’s UNO range; screw sizes are typical, not maker figures. For the portfolio’s canonical wall-plug drill-bit reference, see our wall plug drill bit size guide, and always follow the manufacturer’s data for safety-critical fixings.
Wall Plug Size Chart — Complete UK Reference
| Plug Colour | Plug Diameter | Drill Bit Size | Screw Gauge (No.) | Screw Diameter (mm) | Recommended Screw Length |
|---|---|---|---|---|---|
| Yellow | 5mm | 5mm | No. 4–8 | 3.0–4.0mm | 25–40mm |
| Red | 6mm | 6mm | No. 6–10 | 3.5–5.0mm | 30–50mm |
| Brown | 7mm | 7mm | No. 8–14 | 4.0–5.5mm | 40–70mm |
| Grey (Rawlplug UNO 10mm) | 10mm | 10mm | No. 14–18 | 6.0–8.0mm | 60–100mm |
Recommended Drill Bit Sets
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Free printable Drill Bit & Wall-Plug Chart (PDF)
Every plug colour, drill size and fixing — one sheet for the toolbox.
- All 4 sizing systems cross-referenced
- UK wall-plug colour → exact drill size
- Tap & clearance holes for M3–M12
Plug colours on this page follow Rawlplug’s UNO range (yellow 5mm, red 6mm, brown 7mm, blue 8mm, grey 10mm). Other brands use different colours, so go by the diameter printed on the plug or box.
Load figures are not listed here because a plug’s capacity depends on the product and the wall it goes into, not on its colour. See the substrate-by-substrate load table, sourced from fischer’s published figures.
A note on colour: wall-plug colour is a manufacturer convention, not a British Standard. The sizes above follow Rawlplug’s UNO range, in which blue is 8mm and grey is 10mm (there is no 12mm UNO), while fischer’s DuoPower is grey and red at every size, so its colour tells you nothing about the size at all. Always check the diameter printed on the packet rather than trusting the colour.
Get the free Drill Bit & Wall-Plug Size Chart (PDF)
Every drill size, wall-plug colour & tap size on one printable sheet.
Important notes:
- Published loads depend on the wall. For example, Rawlplug’s recommended tension load for a 6mm UNO plug is 0.71 kN in solid brick but 0.08 kN in aerated concrete.
- Always use at least two fixings for any wall-mounted item. Maker loads are per individual fixing.
- The screw should be long enough to pass through the item being fixed and the full length of the plug; follow the screw length or minimum hole depth the plug maker gives (Rawlplug gives 38mm minimum hole depth for the 6mm UNO, for example).
How the Sizing System Works
The UK wall plug system is beautifully simple once you understand the logic: for standard nylon plugs such as Rawlplug UNO, the drill bit diameter equals the plug diameter. A 6mm red plug goes into a 6mm hole drilled with a 6mm masonry bit. The screw then goes inside the plug and expands it against the sides of the hole, creating a friction grip in the masonry.
The screw gauge determines how much the plug expands. Too thin a screw and the plug won’t grip properly. Too thick and you’ll split the plug or struggle to drive the screw home. The chart above gives the correct gauge range for each plug size.
Screw Gauge to Millimetre Conversion
UK screws are sold in both gauge numbers and metric sizes, which causes endless confusion. Here’s the conversion table:
| Screw Gauge (No.) | Diameter (mm) | Common Uses |
|---|---|---|
| No. 4 | 2.9mm | Small hinges, light brackets, cable clips |
| No. 6 | 3.5mm | Light shelving, small hooks, switch plates |
| No. 8 | 4.0mm | General purpose — shelves, curtain poles, most brackets |
| No. 10 | 5.0mm | Heavier brackets, TV mounts, handrails |
| No. 12 | 5.5mm | Heavy-duty brackets, gate hinges |
| No. 14 | 6.0mm | Coach screw applications, structural brackets |
Choosing the Right Screw Length
The screw must be long enough to pass through three things:
- The item being fixed — the bracket, shelf support, or mounting plate
- The full length of the wall plug — so the screw engages the entire plug
- Any extra length the plug maker specifies — so the screw fully expands the plug
For example, add the bracket thickness to the plug length and any extra the plug maker specifies to find the shortest screw you can use.
Drill Bit Types — Which Bit for Which Wall?
| Wall Material | Drill Bit Type | Drill Setting | Notes |
|---|---|---|---|
| Solid brick | Masonry bit (TCT tip) | Hammer drill mode | Standard approach — use hammer action for best results |
| Concrete / dense block | Masonry bit (TCT tip) | Hammer drill mode | May need SDS drill for reinforced concrete |
| Lightweight block (thermalite) | Masonry bit (TCT tip) | Drill mode only (no hammer) | Hammer action can crumble the block — drill gently |
| Plasterboard | HSS or wood bit | Drill mode only | Expansion-only masonry plugs are not designed for plasterboard; use plasterboard fixings or a universal plug with a published plasterboard load (Rawlplug lists one for the UNO) |
| Tile (over masonry) | Tile/glass bit, then masonry bit | Drill mode through tile, then hammer | Start with tile bit to prevent cracking, switch to masonry once through |
| Timber / stud | HSS or wood bit | Drill mode | No wall plug needed — screw directly into timber |
A good masonry drill bit set covering 5mm, 6mm, 7mm, 8mm, and 10mm will handle virtually any wall plug job. Check price on Amazon
When to Use Each Plug Size
Yellow Plugs (5mm) — Light Duty
Yellow plugs are for light loads only. Think picture hooks (for lightweight frames), cable clips, small decorative brackets, and thermostats. For anything heavier than light picture frames and similar, step up to red plugs.
Common mistake: Using yellow plugs for smoke detectors or carbon monoxide alarms on ceilings. Ceiling fixings are under constant gravitational pull — use red plugs for anything mounted overhead.
Red Plugs (6mm) — General Purpose
Red plugs are the UK’s workhorse fixing. They handle the majority of household tasks: curtain pole brackets, towel rails, bathroom accessories, shelving brackets (for lightly loaded shelves), coat hooks, and light-to-medium wall-mounted cabinets.
As a guide, Rawlplug’s recommended tension load for a 6mm (red) UNO plug in solid brick is 0.71 kN; check the load for your plug and wall. Fischer plug assortment — check price on Amazon
Brown Plugs (7mm) — Heavy Duty
When the job is structural or the load is significant, brown plugs are your go-to. TV wall mounts, heavy floating shelves, boiler flue brackets, garden trellis battens, wall-mounted towel radiators, and kitchen wall cabinets all call for brown plugs.
As a guide, Rawlplug’s recommended tension load for a 7mm (brown) UNO plug in solid brick is 0.86 kN. Capacity depends on the plug brand and the wall it goes into — see the substrate-by-substrate load table on our masonry wall plugs guide for the published figures. Fischer plug box — check price on Amazon
10mm Plugs (Rawlplug UNO Grey) — Extra Heavy Duty
10mm plugs suit heavier domestic fixings such as heavy shelving, radiators and large wall cabinets, within their published loads (Rawlplug gives 1.00 kN per 10mm UNO plug in solid brick, tension). They are not a structural fixing: external handrails, balustrades, security gates and anything else whose failure could cause a fall need a through-bolt, a sleeve or expansion anchor, or a resin anchor with a published ETA — neither Rawlplug nor fischer lists those applications for a nylon plug. In commercial settings, they’re used for signage, equipment mounts, and heavy racking.
Blue plugs require a 10mm hole, which means a decent hammer drill or SDS rotary hammer. A standard cordless combi drill can manage 10mm in brick but will struggle in dense concrete.
Pro Tips for Perfect Fixings Every Time
- Mark the drill depth: Wrap a piece of masking tape around the drill bit at the correct depth so you don’t drill too deep or too shallow.
- Vacuum the hole: Dust left in the drilled hole reduces the plug’s grip. A quick blast with a vacuum nozzle makes a real difference.
- The plug should be a firm push fit: If it slides in loosely, the hole is oversized — try the next plug size up, or use a chemical anchor.
- Don’t over-tighten: Once the screw is snug and the bracket doesn’t move, stop. Over-tightening can spin the plug in the hole and destroy its grip.
- Avoid drilling near edges: Minimum edge distance scales with plug size, so there is no single figure. fischer publishes minimum edge distances in concrete for its DuoPower plugs of 30mm (5×25), 35mm (6×30), 50mm (8×40), 65mm (10×50) and 80mm (12×60). Too close to an edge and the brick splits, and the fixing can fail suddenly well below its rated load. Never drill into mortar joints either — no manufacturer publishes a load rating for a fixing set in a bed joint, so it is unrated there.
- Use a detector first: Always scan for pipes and cables before drilling, especially in kitchens, bathrooms, and above/below sockets and switches. Stud & pipe detector — check price on Amazon
Watch: Video Guide
Frequently Asked Questions
What size drill bit for a red wall plug?
A red wall plug requires a 6mm masonry drill bit. For standard nylon plugs the drill bit size matches the plug diameter: red (UNO) plugs are 6mm, so you need a 6mm bit. Use the screw size given on the plug packaging.
What size drill bit for a brown wall plug?
A brown wall plug requires a 7mm masonry drill bit. Use the screw size given on the plug packaging. Brown plugs are the go-to choice for heavy fixings like TV mounts and heavy shelving.
What’s the difference between a No. 8 screw and a 4mm screw?
A No. 8 gauge screw has a thread (outside) diameter of about 4.2mm, so in practice they are treated as the same thing. Gauge refers to the thread diameter, not the plain shank — it is the thread crest that expands the plug, so sizing a screw off the shank leaves it too small to grip properly. The UK gauge system (No. 4, 6, 8, 10, etc.) is gradually being replaced by metric measurements, but you’ll still see both on packaging. See our conversion table above.
Can I use a bigger plug if the hole is too large?
No — and this is one of the few places where the obvious fix is the wrong one. Once a hole has been drilled oversize, or has wallowed out while drilling, no manufacturer publishes a load rating for it and the figures in the tables above no longer apply. A larger plug pressed into a torn hole can feel firm going in and then release under sustained load. Either abandon the hole, move at least 50mm away and re-drill, or use an injection (resin) anchor rated for the actual hole diameter — that is the only fixing designed to fill an irregular hole and bond to the masonry.
What if I hit a hard spot while drilling brick?
You’ve likely hit the engineering brick or a piece of flint/aggregate in the concrete. Keep the hammer drill on, apply steady pressure, and let the bit do the work. Don’t force it — this overheats the bit and dulls the cutting edge. If the bit isn’t making progress, try a fresh sharp masonry bit.
Related Guides
- Wall Plug & Fixing Compatibility Guide — Main Hub
- Masonry Wall Plugs & Fixings Guide
- Plasterboard Fixings Guide
- Cavity Wall Fixings Guide
- What Fixings for a TV Mount?
- What Fixings for Curtain Poles?
- What Fixings for Heavy Shelves?
- What Fixings for Heavy Mirrors?
Recommended Wall Plug Kits
Having the right selection of plugs and matching drill bits saves multiple trips to the hardware shop. These kits cover the most common sizes.
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How we compile this guide
We cross-reference compatibility details against manufacturer specifications where available, official tool manuals, and the physical standards that govern fitment (bore sizes, arbor diameters, voltage platforms, connector types). We prioritise primary sources over retailer listings, flag anything we can’t confirm, and re-verify the data on a regular cycle. Where we give a buying recommendation, we tell you the reasoning — not just the link. More on our method →
