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’s a complete reference guide with all the standard UK wall plug sizes, their corresponding drill bits, screw compatibility, and load ratings.
Quick Answer: Wall Plug Sizes and Drill Bits
| Plug Colour | Plug Size (mm) | Drill Bit Size (mm) | Screw Gauge Range | Screw Diameter (mm) | Max Load (Brick) | Common Uses |
|---|---|---|---|---|---|---|
| Yellow | 5 | 5 | #4–#8 | 3.0–4.5mm | ~15 kg | Light shelves, picture hooks |
| Red | 6 | 6 | #6–#10 | 3.5–5.0mm | ~20 kg | Shelving brackets, curtain rail |
| Brown | 7 | 7 | #8–#12 | 4.0–5.5mm | ~25 kg | Heavy shelving, towel rails |
| Blue | 10 | 10 | #12–#16 | 5.0–6.0mm | ~35 kg | TV brackets, heavy mirrors |
| Grey | 12 | 12 | #14–#18 | 6.0–8.0mm | ~45 kg | Boiler brackets, heavy loads |
The golden rule: The drill bit size always matches the plug size. 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: #4 to #8 (metric M3 to M4.5)
Typical screw diameter: 3.0–4.5mm
Load rating: Around 15 kg in brick. Lower in weaker block.
Best for: Light picture frames, small shelves (up to 3 kg per anchor), hooks for light items.
When to use: When weight is light and the hole doesn’t need to be very strong. They’re small, discrete, and cheap.
Common mistake: Using yellow plugs for something heavy. They’ll loosen over time if overloaded.
Red Plugs (6mm)
Drill bit: 6mm
Compatible screws: #6 to #10 (metric M3.5 to M5)
Typical screw diameter: 3.5–5.0mm
Load rating: Around 20 kg in brick.
Best for: Standard shelving brackets (up to 5–8 kg), curtain rail fixings, towel rails (light to medium loads).
When to use: This is the most common size. If you’re not sure, red is usually safe for general-purpose fixings on moderate loads.
Why it’s popular: It’s the Goldilocks of plugs—strong enough for most jobs, not oversized or wasteful.
Brown Plugs (7mm)
Drill bit: 7mm
Compatible screws: #8 to #12 (metric M4 to M5.5)
Typical screw diameter: 4.0–5.5mm
Load rating: Around 25 kg in brick.
Best for: Heavy shelves (10–15 kg), towel rails, medicine cabinets, security fixings.
When to use: When you’re hanging something substantial and need extra security. A step up from red plugs.
Blue Plugs (10mm)
Drill bit: 10mm
Compatible screws: #12 to #16 (metric M5 to M6)
Typical screw diameter: 5.0–6.0mm
Load rating: Around 35 kg in brick.
Best for: Heavy items: TV wall brackets (20–30 kg), large mirrors, heavy radiators, kitchen extraction units.
When to use: For anything that would be disastrous if it fell. Blue plugs are strong and reliable.
Grey Plugs (12mm)
Drill bit: 12mm
Compatible screws: #14 to #18 (metric M6 to M8)
Typical screw diameter: 6.0–8.0mm
Load rating: Around 45 kg in brick.
Best for: Heavy industrial fixings: boiler brackets, large cabinets, security equipment.
When to use: Heavy commercial installations or when maximum security is needed. Overkill for most home use but worth it for critical items.
How to Choose the Right Wall Plug Size
Step 1: Estimate the weight of what you’re hanging.
Step 2: Calculate load per anchor. If you’re using two anchors, divide the weight by 2. If three anchors, divide by 3.
Step 3: Choose plug size based on load. Use the table above as a guide. For safety, pick one size up (e.g., red instead of yellow).
Examples
Hanging a 10 kg mirror with 2 brackets: 5 kg per anchor. Use red (20 kg) or brown (25 kg) plugs. Red is fine, brown is safer.
Mounting a 25 kg TV with 2 brackets: 12.5 kg per anchor. Use blue (35 kg) plugs. Never use red.
Shelving 15 kg books on 3 brackets: 5 kg per anchor. Use red (20 kg) plugs. This is within safe limits.
Rule of thumb: Pick a plug rated 1.5× the expected load per anchor. This gives safety margin for wear and aging.
Screw Compatibility
Wall plugs expand to fit a range of screw sizes. Here’s how:
Yellow plug (5mm): Use screws #4 to #8. These are thin screws (3.0–4.5mm diameter). A #4 might be loose, a #8 might be tight, but anywhere in the range works.
Red plug (6mm): Use screws #6 to #10. The most common range. A #8 wood screw (4mm diameter) is typical.
Brown plug (7mm): Use screws #8 to #12 (4–5.5mm diameter).
Blue plug (10mm): Use screws #12 to #16 (5–6mm diameter). Heavy-duty screws.
Grey plug (12mm): Use screws #14 to #18 (6–8mm diameter). Very thick screws.
Important: The screw type (wood, machine, etc.) doesn’t matter as much as the diameter. A wood screw or machine screw of the same diameter will work in the same wall plug.
Amazon: Wall Plug Assortment Sets on Amazon UK
Load Ratings: What Affects Them?
Wall plug strength depends on three factors:
1. Wall Material
Solid brick (ideal): Full load rating as per table above.
Lightweight block (modern blocks): 50–70% of rated load. They’re weaker than brick.
Aerated block (very weak): 25–50% of rated load. Use oversized plugs or distribute load across multiple anchors.
Concrete: Similar to brick—full ratings.
Mortar between bricks (not ideal): Always drill through mortar into brick, not into the mortar joint itself. The plug needs something hard to grip.
2. Age and Condition
Old mortar and weak walls reduce load capacity. If the wall is crumbly or soft, use larger plugs and multiple anchors.
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: Always use drill bit the same size as the plug. If the hole is already too big, use a larger plug (e.g. red instead of yellow).
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 plug doesn’t grip securely. Load capacity is very low.
Cause: Drilling in the mortar joint between bricks instead of into the brick itself.
Fix: Always drill into the brick, not the mortar. Mortar is much softer and won’t hold the plug.
Using Undersized Plugs for Heavy Items
Problem: Shelf or bracket sags or falls after months.
Cause: Underestimating weight or choosing too-small plugs.
Fix: Use oversized plugs or more anchors. Use the 1.5× safety factor rule.
Plugs for Cavity Walls (Plasterboard)
Problem: Plug spins loose in the wall.
Cause: Wall plugs work by gripping solid material (brick, block, concrete). In a hollow wall cavity, there’s nothing to grip.
Fix: Never use Rawl plugs in cavities. Use cavity wall fixings (spring toggles, butterfly anchors, self-drill fixings) instead.
Installing Wall Plugs: Step-by-Step
- Choose plug size based on weight (see table above)
- 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)
- Drill straight into the brick (not into mortar). Use moderate speed (800–1500 RPM).
- Drill deep enough for the plug. Plugs typically sit fully inside the wall (5mm plug = 5mm hole, 10mm plug = ~12mm deep).
- 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 UK
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?
The drill bit size always matches the plug size. 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’re different sizes rated for different loads. Yellow (5mm): ~15 kg. Red (6mm): ~20 kg. Brown (7mm): ~25 kg. Blue (10mm): ~35 kg. Grey (12mm): ~45 kg. Choose based on what weight you’re hanging. For safety, pick one size up (e.g., use red instead of yellow if you’re on the border).
How much weight can a wall plug hold?
It depends on the plug size and wall material. In solid brick: yellow ~15 kg, red ~20 kg, brown ~25 kg, blue ~35 kg, grey ~45 kg. These are maximums per anchor. Weak or old block walls will hold less. Always use multiple anchors for heavy items (distribute the load) and allow safety margin by choosing plugs rated higher than your estimated load.
Can I use wall plugs in plasterboard?
No. Wall plugs work by gripping solid material like brick or block. In plasterboard cavities, there’s nothing for the plug to grip—it will spin and loosen. For plasterboard, use cavity wall fixings instead (spring toggles, butterfly anchors, or self-drill cavity fixings).
What happens if the drill hole is too big?
The wall plug will spin and won’t grip securely. The screw will loosen over time and the item will fall. Solution: always use the correct drill bit size. If the hole is already too big, insert a larger plug (e.g., use a red plug instead of yellow) or fill the hole with filler and re-drill.
Can I drill into mortar instead of brick?
You *can*, but you shouldn’t. Mortar is much softer than brick and won’t hold the plug securely. Load capacity drops dramatically. Always drill into the brick itself, not the mortar joints between bricks. This gives maximum grip and strength.
How many wall plugs do I need for a shelf?
At least 2, ideally 3 for long shelves. Distribute the load evenly across all anchors. A 15 kg shelf on 2 anchors = 7.5 kg each, which requires red or brown plugs. Spread across 3 anchors = 5 kg each, which red plugs can handle. More anchors = safer distribution.
