Using the wrong drill bit is one of the most common DIY mistakes — it produces poor results, damages surfaces, and puts unnecessary strain on your drill. The right bit makes drilling faster, cleaner, and easier. Here's everything you need to know.
The Most Important Rule
Always match the drill bit to the material you're drilling AND to your drill type. A wood bit in masonry will go nowhere. An SDS bit in a standard chuck won't fit. Get the combination right and drilling becomes effortless.
Types of Drill Bit by Material
Masonry Bits (Concrete, Brick, Block): Masonry bits have a hardened tungsten carbide tip that can withstand the impact and abrasion of drilling into hard materials. They're used with the hammer action on a combi drill or SDS drill.
Wood Bits: Several types for different wood drilling applications:
Standard twist bits — the most common type, suitable for drilling clean holes in softwood, hardwood, and sheet materials. Use in drill mode only — never hammer mode.
Flat/spade bits — for larger diameter holes in wood (typically 16-38mm). Fast but less clean than other types.
Forstner bits — produce clean, flat-bottomed holes. Ideal for furniture making, hinge recesses, and any application requiring a precise, clean hole.
Auger bits — long bits for deep holes in timber — used by electricians and plumbers for running cables and pipes through joists.
Hole saws — for large diameter holes (typically 25-150mm) — used for door locks, pipe holes, and cable entry points.
Metal Bits (HSS — High Speed Steel): HSS bits are designed for drilling into metals. They can also be used in wood and plastic but masonry will quickly destroy them.
Multi-Material Bits: Some modern bits are designed to drill wood, metal, and plastic — a useful general-purpose option if you're only buying one set.
Choosing the Right Size
Drill bit size should match the fixing or plug you're using:
| Wall Plug | Drill Bit Size |
|---|---|
| Red plug | 6mm |
| Brown plug | 7mm |
| Blue plug | 10mm |
| Yellow plug | 5mm |
For wood screws — drill a pilot hole slightly smaller than the screw shank to prevent splitting. For clearance holes (where the screw passes through freely) drill the same diameter as the screw shank.
Standard vs SDS Drill Bits — What's the Difference?
Standard round shank bits fit into a standard keyless chuck — used with combi drills for most everyday drilling tasks including masonry with hammer action up to approximately 16mm.
SDS-Plus bits have a slotted shank that locks into an SDS chuck. The bit slides back and forth in the chuck during drilling — transferring more impact energy directly to the drill tip rather than absorbing it in the chuck. For serious masonry drilling above 16mm or for drilling into reinforced concrete and hard stone, SDS-Plus gives significantly better performance.
SDS-Max bits have a larger shank for use in SDS-Max demolition hammers — for the heaviest breaking and large core drilling work.
Drill Bit Coatings
| Coating | Benefit |
|---|---|
| Bright (uncoated) | Standard HSS — general purpose |
| Black oxide | Reduced friction, better heat resistance |
| Titanium (TiN) | Harder surface, longer life |
| Cobalt (HSS-Co) | Best for stainless steel and hard metals |
Pro Tips for Better Drilling:
Mark your hole first: Use a pencil mark and a centre punch (for metal) to prevent the bit from wandering on start-up.
Start slow: Begin drilling at slow speed to establish the hole position, then increase speed once the bit is cutting.
For tiles: Use a tile bit (diamond or carbide tipped) at slow speed with no hammer action. Masking tape over the drill point prevents the bit skating across the tile surface.
For glass: Use a diamond or carbide glass bit at very slow speed. Keep the bit and glass cool with water.
Withdraw regularly: When drilling deep holes, withdraw the bit every 10-15mm to clear the swarf (waste material). This prevents the bit binding and breaking.
Use the correct speed:
Let the bit cool: HSS bits overheat quickly in metal. Drill for a few seconds then pause to allow cooling. A drop of cutting oil dramatically extends bit life when drilling metal.
Storing Drill Bits
Browse TEH cordless drills, SDS hammer drills and accessories at tehtools.co.uk
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