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Drilling through a block wall is usually easy until the hole needs to be deep, straight, and clean. A short masonry bit may start well, then run out of flute length before the anchor is fully seated. Long bits solve that problem, but they also flex more, wander at startup, and put greater demands on the drill.
For most homeowners, the best choice is a carbide-tipped masonry bit between 8 and 12 inches long, matched to the wall anchor and the drill being used. For repeated holes or large diameters, an SDS-plus bit is usually a better investment than a long straight-shank bit.
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Choosing the Right Bit Length
Bit length is often described as overall length, but the useful measurement is flute length—the portion that can clear dust from the hole. A bit listed as 12 inches long may have only 7 or 8 inches of fluting, with the rest used by the shank.
Measure the required hole depth, then add at least 1 inch for dust clearance and working room. For example, a 4-inch sleeve anchor hole generally calls for a bit with around 5 inches of usable flute length. If you are drilling through an 8-inch block wall, a 12-inch or longer bit may be necessary, especially if the hole must pass completely through the block.
Do not automatically buy the longest bit available. A 16-inch bit is more prone to deflection and is harder to keep square. Use the shortest bit that reaches through the wall and leaves room for debris to escape.
Straight-Shank Versus SDS Masonry Bits
| Bit type | Best use | Advantages | Limitations |
|---|---|---|---|
| Long straight-shank carbide bit | Occasional holes in block, brick, or soft concrete | Inexpensive; works in a standard chuck; suitable for smaller holes | Can slip in a chuck; slower drilling; more likely to wander or bind |
| SDS-plus masonry bit | Multiple holes and medium-duty anchor work | Positive drive; efficient dust removal; better impact transfer | Requires an SDS drill; usually costs more |
| SDS-max bit | Large holes and heavy concrete work | Very strong; handles large diameters and demanding drilling | Overkill for most block-wall anchors; needs a larger rotary hammer |
A straight-shank bit is fine for a few holes in hollow concrete block, particularly in the 1/4- to 1/2-inch range. Look for a three-flat or hex shank if your drill chuck tends to lose grip. A smooth round shank can spin under load, damaging both the bit and the chuck jaws.
For a larger project, an SDS-plus long masonry bit set is generally the more practical choice. SDS bits lock into the tool, allowing the shank to slide slightly while still transferring hammer blows. That makes them faster and less tiring than forcing a standard drill chuck through every hole.
Match the Bit to the Drill
Use a hammer drill or rotary hammer for masonry. A regular cordless drill can make a small hole in soft block, but it will be slow and may overheat when drilling deep. For a few 1/4-inch holes, a hammer drill with a masonry bit is usually enough. For holes above 1/2 inch, deep holes, or more than a handful of anchors, a rotary hammer is the better tool.
Use the drill’s hammer mode only with bits designed for hammer drilling. Carbide-tipped masonry bits are not interchangeable with ordinary twist drills. The carbide cutting edge breaks up the mineral material, while the flutes carry dust out of the hole.
For a standard cordless hammer drill, keep the speed moderate and let the carbide tip do the work. Excessive speed creates heat without necessarily improving progress. A rotary hammer should normally run at its recommended hammer-drill setting; pushing harder rarely makes it drill faster and can crack the block web.
Choose Diameter by the Anchor
The anchor package should specify the drill-bit diameter. Follow that instruction rather than sizing the hole by eye. A hole only 1/16 inch too large can leave a plastic anchor loose, while an undersized hole can prevent a sleeve anchor from seating fully.
For light loads such as cable clips, small shelves, or conduit straps, plastic masonry anchors with 1/4- to 5/16-inch holes are often adequate. For heavier loads, use a rated sleeve anchor, concrete screw, or other fastener intended for masonry. Hollow block requires extra caution: an anchor that works in solid concrete may have poor holding power if it lands in a hollow cell.
If you need common sizes for several projects, a long carbide-tipped masonry bit set can be cheaper than buying individual bits. Sets are worthwhile when the sizes are accurate and the bits have enough flute length; a large assortment of short, low-quality bits is not a substitute for one good long bit.
How to Drill Through Block Cleanly
Mark the hole and begin at low speed with the drill held square to the wall. Start without hammer action if the bit wants to skate, then switch hammer mode on once the tip has established a shallow recess. This reduces chipped paint and prevents the hole from starting at an angle.
Every 2 to 3 inches, withdraw the bit while it is still rotating to clear dust. Deep masonry dust can pack tightly around the tip, causing the bit to bind and the drill motor to heat up. If progress suddenly stops, back the bit out rather than leaning harder on the tool.
When drilling through a hollow block, the bit may suddenly break into a void. Reduce pressure at that point so the tip does not punch through and damage the far face. Put a piece of tape on the bit to mark the required depth, and stop as soon as the anchor will sit flush.
When to Replace a Masonry Bit
A masonry bit is worn when drilling takes much longer than usual, the carbide tip looks rounded, or the bit produces fine dust without making useful depth. A slightly dull bit may still work in soft block, but it can overheat a cordless drill and enlarge the hole.
For occasional DIY work, a cheaper straight-shank bit is perfectly reasonable. Spend more on an SDS-plus bit and rotary hammer when you need many deep holes, larger diameters, or consistent results. The tool and bit combination matters more than buying the longest bit on the shelf.