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.
One of the most common DIY questions: “What size drill bit do I need for this wall plug?” The answer is printed on the plug packet, but once you lose that packet, you’re guessing. Here is a reference guide to the common UK wall plug sizes and the drill bit for each, with guidance on screws and on what affects published loads.
This guide does not provide generic safe loads by plug colour. Use the load and installation data for the exact fixing, screw and substrate. Safety-critical, overhead or structural applications need a fixing system specifically documented for that use and an appropriate design; a colour chart cannot establish suitability.
Quick Answer: Wall Plug Sizes and Drill Bits
| Plug Colour | Plug Size (mm) | Drill Bit Size (mm) | Screw Gauge Range | Screw Diameter (mm) | Common Uses |
|---|---|---|---|---|---|
| Yellow | 5 | 5 | As on the packaging | As on the packaging | Select by the exact product’s substrate and application data, not by colour. |
| Red | 6 | 6 | As on the packaging | As on the packaging | Select by the exact product’s substrate and application data, not by colour. |
| Brown | 7 | 7 | As on the packaging | As on the packaging | Select by the exact product’s substrate and application data, not by colour. |
| Blue | 8 | 8 | As on the packaging | As on the packaging | Select by the exact product’s substrate and application data, not by colour. |
| Grey | 10 | 10 | As on the packaging | As on the packaging | Select by the exact product’s substrate and application data, not by colour. |
Recommended Drill Bit Sets
As an Amazon Associate we earn from qualifying purchases. Check fitment & current price on Amazon (affiliate links).
Before you buy: check that the size, fitting/bore and maximum-rated speed marked on the accessory match what your tool’s manual specifies. We have not physically tested these products; listings are compiled from published specifications. These are affiliate links.
Free printable Drill Bit & Wall-Plug Chart (PDF)
Match the right drill bit to every wall plug, every time.
- All 4 sizing systems cross-referenced
- UK wall-plug colour → exact drill size
- Tap & clearance holes for M3–M12
Load figures are not listed here because a plug’s capacity depends on the exact product, screw, substrate and installation. Our masonry load guidance explains the withdrawal of the earlier numeric comparison. Use the manufacturer’s current documentation for the fixing you have.
Colour is a manufacturer convention, not a British Standard. The sizes above follow Rawlplug’s UNO universal plug range, where blue is 8mm and grey is 10mm — Rawlplug does not make a 12mm UNO. Some unbranded and own-label plugs use blue for 10mm instead, and fischer’s DuoPower is grey and red at every size, so its colour tells you nothing about the size. Always check the size printed on the packet rather than relying on the colour.
Get the free Drill Bit & Wall-Plug Size Chart (PDF)
Every drill size, wall-plug colour & tap size on one printable sheet.
The golden rule: For standard nylon plugs such as Rawlplug UNO and fischer SX Plus, the drill bit size matches the plug size; check the drill diameter the maker gives. A 5mm plug needs a 5mm drill bit. A 10mm plug needs a 10mm drill bit. This creates a snug fit.
How Wall Plugs Work
A wall plug (Rawl plug, anchor, expanding plug—they’re all the same thing) is a plastic tube with radial slots. When you screw into it, the plug expands outward and wedges tightly into the hole. The tighter the fit between hole and plug, the stronger the anchor.
This is why hole size matters: If the hole is too big, the plug has nothing to grip and spins. If the hole is too small, you can’t insert the plug.
Detailed Wall Plug Size Guide
Yellow Plugs (5mm)
Drill bit: 5mm
Compatible screws: as given on the plug packaging
Typical screw diameter: as given on the plug packaging
Application: Use the identified UNO size only where its specified screw, substrate, load, edge distance and spacing suit the job. Size and colour alone do not make it safe for a particular fixture.
Common mistake: Using yellow plugs for something heavy. They’ll loosen over time if overloaded.
Red Plugs (6mm)
Drill bit: 6mm
Compatible screws: as given on the plug packaging
Typical screw diameter: as given on the plug packaging
Application: Use the identified UNO size only where its specified screw, substrate, load, edge distance and spacing suit the job. Size and colour alone do not make it safe for a particular fixture.
Brown Plugs (7mm)
Drill bit: 7mm
Compatible screws: as given on the plug packaging
Typical screw diameter: as given on the plug packaging
Application: Use the identified UNO size only where its specified screw, substrate, load, edge distance and spacing suit the job. Size and colour alone do not make it safe for a particular fixture.
Blue Plugs (8mm)
Drill bit: 8mm
Compatible screws: as given on the plug packaging
Typical screw diameter: as given on the plug packaging
Application: Use the identified UNO size only where its specified screw, substrate, load, edge distance and spacing suit the job. Size and colour alone do not make it safe for a particular fixture.
Grey Plugs (10mm)
Drill bit: 10mm
Compatible screws: as given on the plug packaging
Typical screw diameter: as given on the plug packaging
Application: Use the identified UNO size only where its specified screw, substrate, load, edge distance and spacing suit the job. Size and colour alone do not make it safe for a particular fixture.
How to Choose the Right Wall Plug Size
Step 1: Identify the wall — solid brick, block, aircrete, plasterboard or a cavity.
Step 2: Use the fixing maker’s published load for that wall. Match the exact product, screw and substrate grade; there is no reliable load per plug colour. The earlier numeric comparison in our masonry guide has been withdrawn pending reconciliation.
Step 3: Use the exact fixing’s specified drill diameter and minimum depth in the load-bearing substrate, then follow its hole-cleaning, embedment and installation instructions.
For anything whose failure could injure someone — handrails, overhead fixings, heavy or articulating TV arms — use a fixing with a published rating for that use and follow its datasheet.
Screw Compatibility
Each plug takes a range of screw sizes, which the maker prints on the packaging:
Yellow plug (5mm): Use the screw size given on the plug packaging.
Red plug (6mm): Use the screw size given on the plug packaging.
Brown plug (7mm): Use the screw size given on the plug packaging.
Blue plug (8mm): Use the screw size given on the plug packaging.
Grey plug (10mm): Use the screw size given on the plug packaging.
Important: use the screw type and diameter the plug maker specifies. Most nylon plugs are designed for wood or chipboard screws — Fischer DuoPower 8 × 40, article 535455, for example, takes 4.5–6.0mm wood or chipboard screws — so a machine screw of the same diameter is not a like-for-like substitute.
Amazon: Wall Plug Assortment Sets on Amazon
Load Ratings: What Affects Them?
Wall plug strength depends on three factors:
1. Wall Material
Published loads depend on the exact fixing, screw and base material. Match the substrate grade in the manufacturer’s load data; do not transfer a brick value to an unverified block or cavity. Our masonry guide’s earlier numeric comparison has been withdrawn pending reconciliation.
Use the base material and installation method covered by the fixing’s documentation. Do not apply a load tested in brick to an unverified mortar joint. Check the exact fixing and wall construction before choosing the hole location.
2. Age and Condition
If a hole is oversized, damaged, or the plug spins, do not assume a larger plug or general-purpose filler restores the published capacity. Select a repair or an alternative fixing or location whose manufacturer specifies suitability for that substrate and condition. Check hole geometry, edge distances and spacing before loading it.
3. Installation Quality
A loose hole (too big) reduces grip and load capacity. A tight hole (perfect fit) maximizes load. Always use the correct drill bit size.
Common Mistakes with Wall Plugs
Hole Too Big
Problem: The wall plug spins instead of gripping. Screw loosens over time.
Cause: Drill bit larger than plug size. Using 6mm bit for a 5mm plug, for example.
Fix: If a hole is oversized, damaged, or the plug spins, do not assume a larger plug or general-purpose filler restores the published capacity. Select a repair or an alternative fixing or location whose manufacturer specifies suitability for that substrate and condition. Check hole geometry, edge distances and spacing before loading it.
Hole Too Small
Problem: Can’t insert the plug. Forcing it damages the plug.
Cause: Using a smaller bit than the plug size.
Fix: Use the correct bit size. Re-drill with the right size if needed.
Drilling into Mortar Instead of Brick
Problem: The fixing’s published load may not apply to the chosen base material.
Cause: The hole is in a mortar joint whose suitability for this fixing has not been established.
Use the base material and installation method covered by the fixing’s documentation. Do not apply a load tested in brick to an unverified mortar joint. Check the exact fixing and wall construction before choosing the hole location.
Using Undersized Plugs for Heavy Items
Problem: Shelf or bracket sags or falls after months.
Cause: Underestimating weight or choosing too-small plugs.
Fix: Follow the shelf or bracket instructions and use a fixing arrangement documented for the actual load and substrate. The required number and layout depend on the brackets, leverage, fixing specification, edge distances and spacing. Do not assume that adding plugs multiplies the published single-fixing capacity.
Plugs for Cavity Walls (Plasterboard)
Problem: Plug spins loose in the wall.
Some plugs rely on expansion in solid material, while other designs can fold or knot in a suitable board. Expansion-only masonry plugs are not a default plasterboard fixing. Some universal plugs are specified for plasterboard: Fischer lists DuoPower 8 × 40, article 535455, with a minimum panel thickness of 12.5mm. Select the exact fixing for the board construction, thickness and load, and follow its screw and installation requirements.
Installing Wall Plugs: Step-by-Step
- Choose the fixing from the maker’s published load for your wall type
- Get the drill bit matching the plug size (5mm plug = 5mm bit, 10mm plug = 10mm bit)
- Mark the hole position on the wall
- Switch to masonry drill bit if you have different bits (for easier cutting into brick)
- Use the drilling mode, bit and speed specified for the fixing and substrate. Place the fixing in the base material covered by its load data; do not apply brick test values to an unverified mortar joint.
- Use the exact fixing’s specified hole depth in the load-bearing substrate. For the Rawlplug UNO variants tabulated here, minimum depths are 34, 38, 40, 42 and 46mm for sizes 5, 6, 7, 8 and 10mm respectively. These figures do not apply to every plug of the same diameter. Follow the product’s edge-distance, spacing and hole-cleaning requirements.
- Push the plug into the hole with your fingers. It should slide in snugly, not loose or tight.
- Insert the screw into the plug
- Hang your item on the screw and tighten
Amazon: Masonry Drill Bit Sets on Amazon
See also: What Drill Bit for Masonry
See also: What Drill Bit for Plasterboard
See also: Drill Bit Size Chart
Watch: Video Guide
Frequently Asked Questions
What drill bit size do I need for a wall plug?
For standard nylon plugs such as Rawlplug UNO and fischer SX Plus, the drill bit size matches the plug size; check the drill diameter the maker gives. A 5mm wall plug needs a 5mm drill bit. A 10mm plug needs a 10mm bit. This creates a snug fit so the plug grips properly. If you use a bit that’s too big, the plug will spin and loosen. Too small, and you can’t insert the plug.
What’s the difference between yellow, red, brown, blue, and grey plugs?
They are different diameters. In the Rawlplug UNO range this guide follows, yellow is 5mm, red 6mm, brown 7mm, blue 8mm and grey 10mm; other brands may use different colours, so go by the diameter printed on the plug. Size alone does not give a safe load — that depends on the maker’s published figure for your wall type.
How much weight can a wall plug hold?
Use the manufacturer’s recommended load for the exact fixing, screw, substrate grade and installation conditions. We have withdrawn the earlier SX numeric examples because their product and column matching has not been established. Single-fixing loads cannot simply be added: the fixture, load direction, spacing, edge distance and substrate also matter.
Can I use wall plugs in plasterboard?
Expansion-only masonry plugs are not a default plasterboard fixing. Some universal plugs are specified for plasterboard: Fischer lists DuoPower 8 × 40, article 535455, with a minimum panel thickness of 12.5mm. Select the exact fixing for the board construction, thickness and load, and follow its screw and installation requirements.
What happens if the drill hole is too big?
If a hole is oversized, damaged, or the plug spins, do not assume a larger plug or general-purpose filler restores the published capacity. Select a repair or an alternative fixing or location whose manufacturer specifies suitability for that substrate and condition. Check hole geometry, edge distances and spacing before loading it.
Can I drill into mortar instead of brick?
Use the base material and installation method covered by the fixing’s documentation. Do not apply a load tested in brick to an unverified mortar joint. Check the exact fixing and wall construction before choosing the hole location.
How many wall plugs do I need for a shelf?
Follow the shelf or bracket instructions and use a fixing arrangement documented for the actual load and substrate. The required number and layout depend on the brackets, leverage, fixing specification, edge distances and spacing. Do not assume that adding plugs multiplies the published single-fixing capacity.
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 →
