Which Size Masonry Drill Bit for Wall Plugs and Anchors?

The short rule: bit size follows the fixing

A wall plug grips by expanding inside the hole. If the hole is too big, the plug spins and never bites. If it is too small, the plug will not seat, and you may crack the brick or block while forcing it in.

So the first number to find is the plug or anchor diameter, which is printed on the packet or the product page. The screw size matters second. A plug is sized for a range of screws, and the screw expands it once driven.

Most plug and anchor makers print the matching bit size right on the packaging. When that and a chart disagree, trust the packaging, because designs differ between brands.

Quick size table for common fixings

The sizes below are typical values. Treat them as a starting point and confirm against your packet. Metric bits are common for plugs sold in the UK and Europe. US anchors are usually specified in inches.

Red, brown and green plugs

Red plugs are the everyday choice for light fixings such as small shelves and cable clips. A 6 mm bit is the usual match. In soft brick or lightweight block, some people go slightly smaller, around 5.5 mm, so the plug sits tight.

Brown plugs are the next size up. They take a 7 mm bit and a thicker screw, which makes them better for heavier items such as larger shelves and wall brackets.

Green plugs are where people get caught out. There is no single color standard, and the same color can mean different sizes depending on the maker. Read the diameter on the packet and pick the bit that matches it. If you only have a loose plug, measure its body with calipers or hold it against the bit shank, and test in scrap masonry first.

M8 Rawlbolts, Tapcons and heavier anchors

An M8 Rawlbolt is a through-bolt style anchor with an expanding shield. The hole has to fit the shield, not the M8 bolt. A 12 mm bit is the common match, but check the packet. Heavier anchors also need depth. Drill the hole deeper than the anchor length so dust has somewhere to go.

A 1/4 in Tapcon is different, because it cuts its own thread directly into the masonry. That means the hole must be smaller than the screw. The usual bit for a 1/4 in Tapcon is 3/16 in. Using a bit that is too large leaves nothing for the thread to grip.

For wedge, sleeve and other expansion anchors, follow the maker's chart. The bit may be the same as the anchor diameter or larger, depending on the design. One search-result chart lists a 3/8 in bit for a 1/4 in anchor, which fits a sleeve-style anchor but not every type, so confirm yours.

Choosing a set that covers these sizes

Most small jobs fall between 1/8 in and 1/2 in, so a set in that range covers Tapcons, small anchors and many plugs. Based on the published specs on our best masonry drill bits page, several sets list diameters in that span. One Bosch SDS-Plus set lists 3/16 in to 1/2 in with a longest bit of 6 in. A DYRECELVE 12-piece set lists 1/8 in to 0.5 in. A DKIBBITH 10-piece set lists the same 1/8 in to 1/2 in range with a 1/4 in bit included four times.

Both of those last two sets have a 3/16 in bit, so they cover a 1/4 in Tapcon. If you need M8 Rawlbolt holes at about 12 mm, note that 1/2 in is just over 12 mm, so a 12 mm bit is better for that anchor. The widest diameter listed on the page is 0.75 in on an SDS-Plus bit.

These figures come from published specifications, not from our own use. Many makers do not publish diameters at all, so check the size markings before you buy.

Match the bit to your drill

Size is only half of it. The shank has to suit your tool, as our best drill comparison explains in more detail for the drill itself.

If you plan to drill many holes in concrete, an SDS-Plus bit in a rotary hammer is the faster route. For a few holes in brick or block, a hex or 3-flat bit in a standard drill is fine. Some listings, including the DYRECELVE and DKIBBITH sets, say they are not for SDS tools or impact drivers, so read the shank notes.

• SDS-Plus shank: locks into a rotary hammer and is built for repeated impact.
• Hex shank: fits standard chucks and some are listed as hammer drill compatible.
• 3-flat round shank: standard chuck only, and some listings say not for impact drills.

Drilling steps and safety

Good technique keeps the hole the size you intended and protects you.

• Mark the spot and check for hidden pipes and wires with a detector before you drill.
• Wear safety glasses, hearing protection and a dust mask. Masonry dust is harmful to breathe.
• Mark the depth on the bit with tape. Aim for slightly deeper than the plug or anchor length.
• Start at low speed with light pressure, then speed up once the bit bites. Use hammer mode only with bits that allow it.
• Pull the bit out now and then to clear dust, and let it cool between holes.
• Blow or vacuum the hole clean before inserting the plug or anchor.
• Test your bit and plug in a scrap piece when you are unsure, since masonry varies.

Frequently asked questions

Can I use a slightly smaller bit than the plug size?

Only a little, and only in soft material. A tight fit can help in lightweight block, but in hard brick a bit that is too small stops the plug seating and can crack the wall.

Do I need a hammer drill for wall plugs?

Not always. A standard drill with a carbide-tipped bit can handle brick and block. Concrete is much easier with a hammer drill or rotary hammer, as long as the bit allows hammer action.

Why does my plug spin in the hole?

The hole is probably too big, or the wall is crumbly. Try the next plug size up with the matching bit, or use a fixing designed for soft or hollow material.

How deep should the hole be?

Drill deeper than the plug or anchor length, since dust collects at the bottom. Marking the depth on the bit with tape keeps it consistent.