Wall Plugs (Rawlplugs): The Size Matching Guide That Stops Fixings Failing
The UK guide to wall plug sizes, colours, and screw matching. Yellow is 5mm, red is 6mm, brown is 7mm. Get the combination wrong and your shelf hits the floor.
A kitchen wall unit pulls away from the wall at 2am. The mugs are smashed. The plaster's torn out. And the reason, nine times out of ten, is a red wall plug paired with a 3.5mm screw that was too thin to expand it, drilled into a hole that only reached the plaster layer. Three things wrong, one catastrophic result.
Wall plugs are the most common fixing in UK construction and DIY. They're also the fixing most often installed incorrectly. The colour coding system exists to make selection simple, but most people never learn what the colours mean, and even those who do regularly confuse which number matches which part.
One rule fixes everything: the drill bit matches the plug. The screw is 1-2mm smaller. That's it.
What a wall plug is and how it works
A wall plug is a ribbed plastic sleeve that you push into a drilled hole in masonry. When you drive a screw into the plug, the screw's threads force the plastic to expand outward against the sides of the hole. That expansion creates friction grip. The tighter the plug grips the hole wall, the more weight the fixing can support.
The mechanism is simple, but it depends on three things being correctly matched: the hole must be the right diameter for the plug, the plug must be fully embedded in solid material (not plaster), and the screw must be the right gauge to expand the plug properly.
Too thin a screw and the plug barely expands. Too fat and you'll split the plug or push it deeper into the hole. Too wide a drill hole and the plug has nothing to grip against. Too narrow and you can't get the plug in at all.
The ribs and fins moulded into the outside of the plug aren't decorative. They bite into the masonry and prevent the plug from spinning when you drive the screw. Cheap plugs with smooth bodies or shallow ribs are far more likely to spin uselessly in the hole. If you've ever had a plug that just rotates when you try to tighten the screw, that's either a smooth-bodied plug or a hole drilled too large.
Sizes, colours, and the matching table
UK wall plugs follow a colour coding system. Every manufacturer uses the same colours for the same sizes. Learn five colours and you'll never need to read the back of a packet again.
This is the table to bookmark. It answers the question that causes more DIY failures than any other: which drill bit, which plug, which screw.
| Plug colour | Plug diameter | Drill bit size | Screw gauge (imperial) | Screw diameter (metric) | Use for |
|---|---|---|---|---|---|
| Yellow | 5mm | 5mm | No. 4 to No. 8 | 3.0 - 4.0mm | Light loads: picture hooks, cable clips, light switch plates |
| Red | 6mm | 6mm | No. 6 to No. 10 | 3.5 - 5.0mm | Medium loads: shelves, curtain poles, towel rails, brackets |
| Brown | 7mm | 7mm | No. 8 to No. 14 | 4.0 - 6.0mm | Heavy loads: kitchen wall units, boiler brackets, TV mounts |
| Blue | 10mm | 10mm | No. 14+ | 5.0 - 8.0mm | Extra heavy: security gates, large structural brackets |
Read the table left to right. Yellow plug, 5mm drill bit, screws between 3.0 and 4.0mm diameter. Red plug, 6mm drill bit, screws between 3.5 and 5.0mm. Brown plug, 7mm drill bit, screws between 4.0 and 6.0mm. The plug diameter and the drill bit diameter are always the same number.
The two most common combinations in UK DIY and trade work are the red 6mm plug with a No. 8 gauge screw (4mm diameter), and the brown 7mm plug with a No. 10 gauge screw (5mm diameter). Between those two combinations, you can fix almost anything to a masonry wall.
An electrician's trick for a tighter fit in soft block: use a 5.5mm drill bit instead of 6mm for red plugs. The half-millimetre difference gives a noticeably firmer grip in lightweight blocks where a 6mm hole can feel loose.
What the load ratings actually mean
The holding power of a wall plug depends on the plug size, the screw used, and the material you're fixing into. A 6mm red plug in dense concrete holds far more than the same plug in aerated block.
Fischer DuoPower plugs are the premium option, and their published load data shows the difference substrate makes:
| Plug size | Screw range | Concrete | Solid brick | Perforated brick | Aerated block | Plasterboard |
|---|---|---|---|---|---|---|
| 6 x 30mm | 4-5mm | 95 kg | 50 kg | 15 kg | 10 kg | 15 kg |
| 8 x 40mm | 4.5-6mm | 110 kg | 62 kg | 25 kg | 10 kg | 15 kg |
| 10 x 50mm | 6-8mm | 215 kg | 120 kg | 25 kg | 20 kg | 15 kg |
Those numbers explain why wall plugs that work perfectly in one house fall out of the wall in another. A 6mm plug in solid brick holds 50 kg per fixing. The same plug in aerated concrete block holds 10 kg. Five times less. If you're hanging a heavy mirror on two fixings in aerated block, each plug is supporting only 10 kg before you're at the limit.
Types beyond the standard plastic plug
Standard plastic plugs are the basic ribbed sleeves in yellow, red, and brown. They work well in solid masonry. Cheap. Available everywhere. The only type most people ever use.
Fischer DuoPower is the premium universal plug. Two-component nylon construction. In solid walls, it expands like a normal plug. In hollow walls or cavities, it folds and knots behind the plasterboard to create an anchor. This dual action is why it's rated 4.9 out of 5 from over 400 reviews at Screwfix, and why trade forums recommend it repeatedly. It costs more. It's worth more.
Heavy-duty nylon plugs (like the Rawlplug FIX range) are denser and harder-wearing than standard plastic. Better anti-rotation fins, more aggressive ribbing. The right choice when you're fixing into hard masonry or when the load is near the upper limit of the plug size.
Hammer-in fixings combine a plug and nail in one unit. You drill the hole, push in the fixing, and hammer the nail home. Fast for serial installation, like fixing battens to a wall for cladding or insulation boards. Less holding power per fixing than a screw-type plug, but speed matters when you're putting in forty fixings across a wall.
How to drill and install wall plugs
Step one: identify the wall
This matters more than anything else. A wall plug designed for solid masonry will fail completely in plasterboard. And many UK homes have walls that look solid but aren't.
Knock on the wall with your knuckle. Solid masonry gives a dull, dead thud. Plasterboard on stud gives a hollow sound. Dot-and-dab plasterboard on masonry sounds hollow in patches (where the gaps are) and solid in others (where the adhesive dabs sit).
If the wall sounds hollow, don't use standard wall plugs. Use plasterboard-specific fixings or, for dot-and-dab walls, Corefix fixings that bridge through to the masonry behind. Four Corefix fixings can support up to 100 kg.
Step two: drill the hole
Use a masonry drill bit that matches the plug diameter. Red plug, 6mm masonry bit. Brown plug, 7mm masonry bit. Set your drill to hammer action for brick and block. Without hammer action, you'll be there all day and the bit will wander.
Drill 10mm deeper than the plug length. A 30mm red plug needs a 40mm hole. This extra depth allows for drilling dust that falls to the bottom of the hole and gives the screw tip somewhere to go.
Wrap a piece of tape around the drill bit at the target depth so you know when to stop. Or use the depth stop rod if your drill has one.
Step three: clear the dust
Blow into the hole or use a vacuum to remove drilling dust. Dust packed at the bottom of the hole stops the plug seating fully. It also reduces expansion grip because the plug is pushing against loose powder rather than solid masonry.
Step four: insert the plug
Push the plug in with your thumb. It should go in with firm pressure. If it slides in easily, the hole is too big. If you need a hammer, the hole is too tight (which is actually fine for grip, but you risk cracking the plug in hard masonry).
The plug should sit flush with the wall surface. Not recessed, not protruding. Flush.
Step five: drive the screw
Hold your fixture in position, push the screw through the fixture hole into the plug, and drive it home. Use a screwdriver or drill on a low torque setting. As the screw enters the plug, you'll feel resistance increase. That's the plug expanding. Keep going until the screw is tight and the fixture is firmly against the wall.
The screw should be longer than the plug. A 30mm plug with a 40mm or 50mm screw is correct. The screw tip needs to pass through the full length of the plug to expand it properly, plus a few millimetres beyond.
If your plug sits entirely within the plaster layer, the fixing will fail. Plaster is typically 12-15mm thick. A 30mm red plug in a 40mm hole reaches well into the masonry behind. But if you only drill 20mm deep, most of your plug is gripping nothing but crumbly plaster. Check that your drill depth gets past the plaster and into the brick or block behind.
How much do you need
Wall plugs are cheap enough that running short mid-job is the only real waste. Buy more than you think you'll need. A pack of 100 red plugs costs under a pound at budget level. There's no reason to be precise about quantities.
For a kitchen installation with six wall units, you'll use 12-18 brown plugs for the cabinet rail or individual brackets, plus another 10-20 red plugs for miscellaneous brackets, pipe clips, and trim. A 100-pack of each colour covers the kitchen and leaves plenty spare.
For general fixings around a house renovation, a mixed assortment pack is the practical choice. Fischer's 200-piece mixed pack (yellow, red, and brown) costs TBC at Toolstation. The Rawlplug UNO 250-piece mixed pack is TBC at Screwfix.
For a full extension project involving walls and blockwork, fixing battens, brackets, pipe clips, and electrical fittings to masonry walls, buy 200-300 plugs across sizes. The brown 7mm plugs will get used fastest for structural brackets and heavy fittings. Red 6mm for everything else.
Cost and where to buy
Wall plugs split into three pricing tiers. The budget tier is absurdly cheap. The premium tier costs five to eight times more per plug but is dramatically better in difficult substrates.
| Tier | Product | Pack of 100 | Best for |
|---|---|---|---|
| Budget | Easyfix / FandF (own brand) | £0.69 - £1.28 | Solid masonry, straightforward fixings, when you're using hundreds |
| Mid-range | Rawlplug UNO | £2.23 - £2.89 | Good anti-rotation fins, reliable in most masonry, the default trade choice |
| Premium | Fischer DuoPower | £4.99 - £7.99 | Mixed substrates, hollow walls, when you can't identify the wall type, or when failure isn't an option |
Budget plugs from Screwfix (Easyfix brand) start at TBC for 100 yellow 5mm plugs and TBC for 100 red 6mm plugs. At that price, they're essentially disposable. They work fine in solid brick and concrete. They're poor in soft block or anything hollow.
Rawlplug UNO plugs are the trade standard. Better ribbing, better expansion, more consistent sizing. A 100-pack of red 6mm runs TBC at Screwfix. Bulk buys are cheaper: 1,000 red UNO plugs from Toolstation cost TBC, which works out to about 1.5p each.
Fischer DuoPower plugs cost more because they do more. A 100-pack of 6x30mm is TBC at Screwfix. The 8x40mm is TBC. The 10x50mm comes in a 50-pack for TBC. Worth it for any fixing where you're uncertain about the substrate, or where the item being fixed is heavy, expensive, or difficult to reinstall if it falls.
Alternatives: when wall plugs aren't enough
Standard wall plugs have a ceiling. Once you're past it, you need a different fixing entirely. Knowing where that ceiling sits saves you from over-engineering simple jobs and under-engineering heavy ones.
Frame fixings are long screws with a built-in nylon sleeve. You drill through the frame and into the masonry in one operation, push the fixing through, and tighten. Faster than plug-and-screw for fixing door frames, window frames, and timber battens. They hold well in solid masonry and cost around 20-50p each.
Anchor bolts (sleeve anchors, through-bolts) are for loads above 50 kg per fixing point in masonry. Steel construction, mechanical expansion. Used for securing steel brackets, heavy equipment, and structural connections. Overkill for shelves. Essential for things that must never move.
Chemical anchors use a two-part resin injected into a drilled hole, with a threaded rod pushed in before it cures. The resin bonds to the masonry and the rod, creating a fixing that can support hundreds of kilograms. The right choice for crumbly masonry, hollow block where expansion plugs have nothing to grip, or any connection where the load demands it. A cartridge costs TBC, and each cartridge fills multiple holes.
Plasterboard fixings are a separate category entirely. If you're fixing into plasterboard on a stud wall, standard wall plugs won't work. Spring toggles fold flat to pass through a drilled hole and then open behind the board. Gravity toggles drop down behind the board and lock in place. GripIt fixings grip the back face of the plasterboard with metal wings. Metal cavity anchors expand behind the board as you tighten the bolt. Each type holds 15-25 kg in 12.5mm plasterboard. For heavier loads on stud walls, find the timber stud and screw directly into it.
Corefix fixings solve a specific UK problem: dot-and-dab walls. The plasterboard is stuck to the masonry with blobs of adhesive, leaving a 10-25mm void behind the board. Standard wall plugs grip only the plasterboard and pull straight through. Corefix fixings have a steel core tube that bridges the void and transfers load to the masonry. Around £3 – £5 each but rated to 25 kg per fixing.
Masonry screws (Thunderbolt, Tapcon) cut their own thread directly into concrete or brick without any plug at all. Drill a pilot hole, drive the screw. Faster than plug-and-screw, and stronger in hard materials. They struggle in soft block, and they need a specific pilot hole diameter. But for fixing into concrete slabs or dense brick, they're excellent.
Where you'll need this
Wall plugs appear across multiple phases of an extension or renovation:
- Walls and blockwork - fixing battens, brackets, service clips, and fittings to masonry walls throughout the build
- Kitchen installation - securing wall unit brackets or rail to masonry, plus miscellaneous fittings for plinths, end panels, and services
Every time something needs to be attached to a masonry wall, a wall plug is involved. Having the right sizes on site, matched to the right screws, prevents the small delays that add up across a project.
Common mistakes and how to avoid them
Wrong size combination
This is the single most common DIY error in the UK. People buy red plugs and pair them with whatever screws they find in the drawer. A 3mm screw in a 6mm plug barely expands it. A 6mm screw in a 6mm plug splits it. The screw must be 1-2mm smaller than the plug diameter. Check the table. Every time.
Fixing into plaster only
Plaster is 12-15mm thick and has almost zero structural strength. If your plug sits entirely within the plaster layer, the fixing holds only until someone leans on it. Drill deep enough to get the full plug length into the masonry behind the plaster. For a 30mm red plug, that means drilling at least 45mm from the wall surface: 15mm of plaster plus 30mm into brick.
Plug spinning in the hole
You're driving the screw and the whole plug just rotates. Two possible causes. The hole is too large for the plug, so there's nothing for the ribs to bite into. Or the plug is a cheap smooth-bodied type with no anti-rotation features.
Fix it by going up one plug size. Pull the spinning plug out, push in a brown 7mm plug instead of the red 6mm. The brown plug will grip the oversized hole. If you can't go up a size (because the screw hole in your bracket is too small for a larger screw), drill a fresh hole 30mm to the side and start again.
Hole too big from drill wander
The drill bit catches the edge of a mortar joint and the hole ends up 8mm instead of 6mm. Extremely common, especially transitioning from soft plaster into harder brick. Use a smaller pilot bit first (4mm), then open it up to 6mm with the correct bit. The pilot hole guides the larger bit and prevents wander.
Not clearing dust from the hole
Drilling masonry produces a surprising amount of fine dust. It packs into the bottom of the hole and stops the plug seating fully. The plug sits proud of the wall, the fixture doesn't pull tight, and the screw never fully engages the plug. Blow the dust out. Takes three seconds.
Trying to fix a failed hole with filler
Standard decorating filler crumbles the moment a plug tries to expand inside it. If a hole has failed, don't fill it and re-drill in the same spot. Drill a fresh hole 30mm away. If you absolutely must reuse the same location, use a grip-fill adhesive (not decorator's filler), let it cure for at least four days, then re-drill. But moving 30mm to the side is faster, cheaper, and more reliable.
Drilling into mortar joints
Mortar is softer than brick. A plug in mortar holds less weight and is more likely to work loose over time. Aim for the centre of the brick face whenever possible. If you hit a mortar joint, move the hole. A 30mm shift up, down, or sideways is invisible behind most fixtures and makes the difference between a fixing that holds and one that slowly works its way out.
Wall plugs are not complicated. Three numbers in the right order, a clean hole at the right depth, and a plug that matches the wall type. Get those right and your fixings will hold for decades. Get them wrong and you'll be sweeping broken mugs off the kitchen floor at 2am, wondering where it all went wrong.