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Hard aggregate concrete changes the bit-buying decision. The cement is rarely the only problem: crushed granite, flint, river stone, and embedded rebar can all slow drilling or destroy a cheap masonry bit. For occasional anchor holes, a carbide-tipped bit in a hammer drill may be enough. For repeated holes, large diameters, or dense concrete, an SDS-plus rotary hammer and a purpose-built concrete bit are usually the better investment.
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Choose the Right Bit Type
Standard masonry bits have a carbide tip brazed to the end of a steel shaft. They work with a regular drill set to hammer mode and are inexpensive, especially in sizes from 1/4 to 3/8 inch. They are fine for a few holes in ordinary block, brick, or relatively soft concrete.
Hard aggregate exposes their limits. The tip can become dull quickly, the brazed joint can loosen from heat and impact, and the flutes may carry dust poorly. A cheap bit that takes 30 seconds to drill a hole in soft concrete may take several minutes in dense aggregate.
For serious concrete work, use SDS-plus four-cutter concrete bits. Their carbide head has multiple cutting edges and is designed for rotary hammers. Four-cutter designs are less likely to jam when they encounter hard stone and are better suited to occasional rebar contact than two-cutter bits.
| Bit type | Best use | Typical limitation |
|---|---|---|
| Carbide masonry bit | A few small anchor holes | Slow in hard aggregate; wears quickly |
| SDS-plus two-cutter bit | General concrete drilling with a rotary hammer | Can bind or chip when hitting rebar or large stone |
| SDS-plus four-cutter bit | Hard concrete, repeated holes, occasional rebar contact | Costs more than basic bits |
| SDS-max bit | Large holes and heavy demolition-class rotary hammers | Requires a larger SDS-max tool; excessive for small anchors |
Match the Bit to the Tool
A hammer drill and a rotary hammer are not the same tool. A hammer drill uses a mechanical clutch to create a light hammering action. It is compact and useful for occasional 1/4-inch or 5/16-inch holes, but it transfers much less impact energy than a rotary hammer.
A rotary hammer uses a piston mechanism and generally drills hard concrete faster with less pressure from the operator. An SDS-plus tool is the practical choice for holes up to roughly 1 inch in diameter. For large anchor holes, core drilling, or long rows of holes, consider a cordless SDS-plus rotary hammer. Battery tools are convenient, but drilling dense concrete consumes charge quickly; a corded model can be cheaper for stationary work.
Do not use an SDS bit in a regular chuck unless the bit is specifically supplied with a compatible adapter. The connection will slip, run inaccurately, and may damage the chuck. Likewise, do not use a smooth-shank masonry bit in an SDS tool if the bit is not rated for hammering.
What to Look for in a Concrete Bit
Look for a solid carbide head or a clearly stated four-cutter head when drilling hard aggregate. A full-head carbide design is more durable around dense stone and is less likely to snag on rebar than a narrow, two-edge tip. It still is not a rebar-cutting bit; steel can damage any concrete bit if you continue forcing it.
Flute design matters. Deep, open flutes remove powdered concrete and reduce heat. For holes deeper than about 3 inches, periodically withdraw the bit to clear dust. Packed dust turns the hole into a brake, increases heat, and can prevent an anchor from reaching its required embedment depth.
Buy the diameter required by the anchor manufacturer, not merely the diameter printed on the package. A 3/8-inch wedge anchor, sleeve anchor, and concrete screw may each require different hole sizes. For concrete screws, a dedicated concrete screw bit set is useful because it includes common pilot diameters and often fits the same SDS chuck.
Drilling Hard Aggregate Without Burning the Bit
Mark the hole and check for wiring, plumbing, post-tension cables, and embedded steel before drilling. Start the hole at low speed with the tool square to the surface. Once the tip has formed a shallow track, increase speed while keeping steady, moderate pressure. Let the hammer mechanism do the work; pushing hard does not make the carbide cut faster.
For a typical 3/8-inch anchor hole, drill at least 1/2 inch deeper than the anchor’s required embedment. That leaves room for dust below the fastener. Keep the bit moving and withdraw it every 10 to 20 seconds in deep or unusually hard material. Stop if the bit becomes too hot to touch, the motor slows sharply, or the hole stops producing dust.
If the bit hits solid metal, do not lean harder on it. A four-cutter bit may pass through light wire mesh, but repeated contact with rebar calls for a rebar-cutting bit or a new hole location. Switching between hammering and rotation-only modes can help identify what you hit, but never use a concrete bit to deliberately drill structural reinforcing steel.
When the Cheaper Bit Is Enough
A basic carbide masonry bit is the sensible choice for two or three small holes in a garage slab, porch step, or concrete block. If the holes are 1/4 inch or smaller and only 1 to 2 inches deep, spending several times more on premium SDS bits may not improve the result enough to justify the cost.
Upgrade to SDS-plus four-cutter bits when the concrete contains visibly hard stone, when a hammer drill stalls, or when you need more than about a dozen holes. Replace a bit when the tip is visibly rounded, the hole diameter is undersized, or drilling speed has dropped dramatically. A new bit is cheaper than a loose anchor, a burned drill, or a hole that cannot achieve the specified depth.
Buying Recommendation
For occasional small anchors, buy a modest carbide masonry set in the exact diameters your anchors require. For hard aggregate and cordless rotary-hammer work, buy individual SDS-plus four-cutter bits rather than the largest bargain assortment. Choose the diameter and working length carefully, keep a spare for common anchor sizes, and use a vacuum or dust extractor when possible. Cleaner holes improve anchor grip and make the drilling process noticeably faster.