In the UK, most DIY and domestic projects will call for 1 of 4 standard wall plugs. In increasing plug diameter, these are 5 mm (yellow), 5.5 mm (red), 7 mm (brown) and 10 mm (blue).
Using a drill bit with an equivalent size to the plug diameter is often suggested (i.e. a 7 mm drill bit fits a 7 mm plug) but there are crucial exceptions to this rule!
In the UK, wall plugs are sold using various terms including “rawl plugs”, “rawlplugs” and “ fixing plugs”. Wall plugs can be made from plastic, nylon or zinc-plated metals (to resist corrosion and rusting).
To confidently match wall plugs to drill bits, you must be aware of 4 different measurements: plug diameter, plug length, screw diameter and drill bit size. These should be written on your wall plug’s packaging.
If the precise screw and wall plug measurements aren’t available, you could use a ruler, measuring tape or screw sizing guide instead.
Topics
Important Measurements
Plug Diameter
The diameter of the plastic wall plug measured across the inside of the wall plug.
Plug Length
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The length, in millimetres, from the wall plug’s tip to the other end of the plug.
Screw Diameter
Screw diameter is usually measured in millimetres but “screw gauges” are sometimes used instead. Screw gauges are imperial measurements that don’t always have exact metric equivalents.
To fix this, it’s standard practice to round up to the nearest 0.5mm when converting to metric. For example, an 8 gauge screw has a “true” diameter of 4.2 mm but this is rounded up to 4.5 mm.
Drill Bit Size (Drill Diameter)
The drill bit size is the maximum diameter of the drill head (i.e. a power drill or a screwdriver) that can be used.
You can get away with using smaller drill sizes than necessary. However, the grip between the screw and drill head reduces significantly as the drill bit size decreases.
Using a drill bit that’s too small will give you less control over the screw as it’s tightened.
On the other hand, using a drill bit that’s too large for a wall plug can cause scraping, tearing and ripping in some wall plugs (particularly smaller fixings made from plastic and nylon)!
Drill Bit Size versus Wall Plug Size Comparison Table
| Drill Bit Size | British Imperial Screw Gauges (equivalent Metric Screw Diameters) | Wall Plug Length | (Typical) Wall Plug Colour | Wall Plug Diameter |
|---|---|---|---|---|
| 5.5 mm | 6, 8, 9 or 10 gauge (3.5 mm, 4 mm, 4.5 mm or 5 mm) | 34 mm | Bright Red | 5.5 mm |
| 7 mm | 10 or 12 gauge (5 mm or 5.5 mm) | 40 mm | Brown | 7 mm |
| 7 mm | 14 gauge (6 mm) | 40 mm | Brown | 8 mm |
| 8 mm | 12 or 14 gauge (5.5 mm or 6 mm) | 40 mm | Grey | 8 mm |
| 5.5 mm | 6, 8, 9 or 10 gauge (3.5 mm, 4 mm, 4.5 mm or 5 mm) | 22 mm | Yellow | 5.5 mm |
| 6 mm | 6, 8, 9 or 10 gauge (3.5 mm, 4 mm, 4.5 mm or 5 mm) | 34 mm | Orange | 6 mm |
| 6.5 mm | 8, 9, 10 or 12 gauge (4 mm, 4.5 mm, 5 mm or 5.5 mm) | 34 mm | Orange | 6.5 mm |
| 10 mm | 12 or 14 gauge (5.5 mm or 6 mm) | 44 mm | Blue or Grey | 10 mm |
| 10 mm (for Coach Screws) | M6 or M8 | 44 mm | Blue | 10 mm |
| 11 mm | 14 gauge or 16 gauge (6 mm or 8 mm) | 54 mm | Green | 11 mm |
| 11 mm (for Coach Screws) | M8 or M10 | 54 mm | Green | 11 mm |
Differences Between Wall Plug Types
There’s a plethora of plugs in production and use globally.
Fortunately, the wall plug fixings manufactured for UK and EU markets are standardised; they come in predefined metric measurements (millimetres, to the nearest 0.5 mm) and sometimes imperial screw measurements (gauge).
The most common types of wall plugs can be split into three categories: universal wall plugs, expansion wall plugs and self-drilling plugs.
Universal Wall Plugs
As their name implies, these plastic or nylon wall plugs can be used in a multitude of scenarios. They can be installed in solid materials, like stone and timber, and in hollow cavities.
They’re usually installed by first drilling a pilot hole. The universal wall plug is then lightly tapped into the pilot hole until flush with the material’s surface.
The correct-sized threaded screw is then screwed into the universal wall plug – consult the drill bit to wall plug comparison table above for further guidance on wall plug sizing!
As the screw twists into the plug, the universal plug’s exterior fins should twist and retract, gripping onto the surrounding material.
More expensive universal plugs will use both nylon and plastic. The two materials deform predictably in different ways.
Modern wall plug designers have exploited this scientific phenomenon to create expansion wall plugs that can twist into strong shapes in a variety of materials.
Expansion Wall Plugs
Expansion plugs are typically manufactured from nylon or plastic.
Unlike their universal counterparts, expansion plugs have fins that separate outwards from one another as the screw moves into the plug. The fins push against the material in all directions.
Expansion wall plugs usually have 2, 3 or 4 fins.
Self-Drilling Wall Plugs
It’s not always practical to drill a pilot hole before installing a wall plug. This is especially the case in soft materials that are prone to cracking, splintering or crumbling.
Self-drilling wall plugs have a large screw at their base: this is preferably made from metal, as the entire wall plug needs to cut cleanly through the material.
These are used in soft stones (i.e. sandstone), timber and to attach plasterboard to stud framework.
Wall Plug Weight Limits
The weight capacity of identically sized wall plugs can vary massively.
For example, you could have two orange-coloured nylon wall plugs – both 34 mm long and 6 mm in diameter. One could be an expansion plug, capable of handling stresses of up to 70 kg or more. The other could be a universal wall plug with a maximum weight capacity of 5 kg or less!
Identifying wall plugs and understanding their maximum weight restrictions is paramount – never skimp on safety.
Frequently Asked Questions
Which drill bit wall plug lasts the longest?
The longevity of wall plugs depends on how and where they’re used.
When they’re unused, wall plugs have a very long shelf life.
Plastic and nylon wall plugs should have a usable life of 20+ years from manufacturing. Light, heat and water can discolour these plugs over time and gradually reduce their strength.
Zinc-coated metal wall plugs can last considerably longer, so long as the zinc coating isn’t compromised by rust.
All wall plugs get weaker over time. Heavier loads will decrease a wall plug’s effective lifespan.
What size drill bit for 6 mm wall plugs?
6 mm wall plugs fit the following screw diameters: 3.5 mm, 4 mm, 4.5 mm and 5 mm.
You should use a 6 mm diameter drill bit to drive threaded screws into 6 mm wall plugs.
What size drill bit do I use for a 10 mm wall plug?
Use a 10 mm diameter drill bit for most 10mm wall plugs; the imperial equivalent is a 14 gauge drill bit. A 10 mm wall plug is likely to be grey or blue in colour.
There are other, larger wall plugs available but it’s unlikely you’ll need to use these in home DIY projects. 11 mm is generally the largest wall plug size carried by high street DIY shops, trade stores and builders merchants.