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The right bit for a concrete slab depends on the hole diameter, depth and drill you own. For most small holes for masonry screws or plastic anchors, a carbide-tipped masonry bit with a round shank is enough. Larger holes or repeated work are better suited to an SDS-Plus rotary hammer and matching SDS-Plus bit. A powerful hammer drill does not turn an ordinary masonry bit into a rotary-hammer bit: the tools use different motions and shanks.
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Match the bit to the tool
A standard drill’s hammer mode makes the chuck and bit pulse forward while rotating. It works for small holes, but requires firm pressure and can be slow in hard concrete. A rotary hammer uses a more forceful impact mechanism, so it removes material faster with less pushing. Its SDS chuck accepts bits with slotted shanks that slide and move slightly inside the chuck.
| Bit type | Fits | Best use | Main trade-off |
|---|---|---|---|
| Round-shank, carbide-tipped masonry bit | Keyed or keyless drill chuck | Occasional holes, commonly 1/4 to 1/2 inch | Slower in hard concrete; the chuck can slip under heavy use |
| SDS-Plus carbide bit | SDS-Plus rotary hammer | Repeated anchor holes and moderate-diameter holes | Requires an SDS-Plus tool; not for a standard chuck |
| SDS-Max bit | SDS-Max rotary hammer | Large or deep holes and demanding work | Oversized for ordinary anchor holes; needs a larger tool |
| Diamond core bit | Specified drill or core rig | Large, clean openings where the bit and setup are suitable | Different technique and higher cost; not a routine anchor-bit choice |
Check the tool manual before buying. SDS-Plus and SDS-Max are not interchangeable, and a round-shank bit will not lock in an SDS chuck unless the tool has an appropriate chuck accessory.
Choose the right bit
For a handful of shallow anchor holes, a round-shank carbide masonry bit is the economical choice. Use the diameter specified for the anchor, not a guess based on the screw. Anchor packaging typically lists the required bit size and minimum hole depth. Too-small holes make anchors difficult to seat; oversized holes reduce their grip.
If you already own a rotary hammer or expect to drill many holes, choose an SDS-Plus carbide bit in the anchor’s specified diameter. SDS-Plus is the common practical choice for household and light construction work. A two- or four-cutter head can help a bit cope with aggregate and reduce the chance that a single cutting edge catches, but it costs more. For a few small holes, a basic carbide bit is often sufficient.
Look for a carbide tip intended for concrete or masonry, not a wood or general-purpose twist bit. The spiral flutes carry dust out of the hole, and a sound carbide tip resists the abrasion that quickly dulls steel. A worn tip drills slowly and can make a hole that runs off-size. Replace a damaged or badly blunted bit instead of forcing the tool harder.
Get diameter and depth right
Match the bit diameter to the fastener instructions. For example, if an anchor calls for a 1/4-inch hole, use that size rather than stepping up “for clearance.” Mark the required depth on the bit with tape, or use the drill’s depth stop. Drill slightly deeper than the anchor’s stated embedment—often around 1/4 inch extra—to leave room for dust, unless the anchor instructions specify otherwise.
Concrete dust compacts at the bottom of a blind hole and can stop an anchor short. Withdraw the bit with the drill running periodically to clear the flutes. After drilling, remove dust with a bulb blower, vacuum, or the cleaning method required by the anchor manufacturer. Do not assume a hole is clean because the bit came out clear.
Drill without damaging the hole
Confirm the slab is safe to drill. Check plans or scan the area for reinforcement, embedded services and post-tensioning. Never drill into a suspected post-tensioned slab without confirming the tendon layout and getting qualified guidance; striking a tendon can cause severe damage and injury.
Start the hole square to the surface at low speed, then use hammer mode for a standard hammer drill or rotary-hammer mode for an SDS tool. Let the bit cut with steady pressure. Leaning hard on the drill can overheat the bit, stall the tool or widen the hole. If progress stops suddenly, withdraw the bit and clear dust. A hard obstruction may be rebar or stone; do not keep hammering blindly. Switch the tool off before inspecting the bit or hole.
Use hearing protection, safety glasses and a suitable dust-control method. Concrete dust contains respirable crystalline silica. A vacuum or dust shroud designed for drilling is preferable to letting dust spread through an occupied space. Avoid soaking the hole unless the tool, bit and anchor instructions allow wet drilling.
What to buy for your job
For a few small holes in a slab, buy one correctly sized, decent-quality carbide masonry bit for your existing hammer drill. A multi-bit set is worthwhile only if you will use several sizes; sets can include sizes that never match your anchors. For dozens of holes, a rotary hammer and SDS-Plus bit usually save time and effort. Renting a rotary hammer can make more sense than buying one for a single project.
Buy only the diameter and length you need. A long bit flexes more and is harder to keep straight, while a short bit may not reach the required embedment. If the hole is deep, choose a bit with enough usable flute length to clear dust—not merely enough overall length to reach the bottom.
Common problems and fixes
The bit spins without cutting: check that hammer mode is on, the bit is suitable for concrete, and the carbide tip is intact. If the tool is a standard hammer drill and the slab is hard, an SDS-Plus rotary hammer may be the practical answer.
The hole is too wide or the anchor spins: the bit may be worn, the drill may have wobbled, or the diameter may be wrong. Replace the bit and follow the anchor’s stated hole size; do not rely on extra adhesive or a larger screw unless the fastening system allows it.
The bit binds or overheats: reduce pressure, withdraw it to clear dust, and let the bit cool. A smoky smell, discoloration or a loose carbide tip means stop and replace it. For routine slab anchors, matching the tool, bit and anchor instructions matters more than buying the most expensive bit.