What is the difference between a masonry bit and an SDS bit?
Both have a carbide tip and they are not the same bit — the shank, the flute and the tip grind are all built for different amounts of energy.
- Difficulty
- beginner
- Time
- 10 min
- Read
- 3 min
Short answer
A masonry bit has a smooth round shank for an ordinary chuck and a shallow flute, and it is designed for the light rattling percussion of a combi drill. An SDS bit has a grooved shank that locks into the tool and slides, deeper flutes to clear far more dust, and a tip built to survive a piston-driven blow. Neither works properly in the other tool.
People assume the difference is only the shank, buy an adaptor and expect the same performance. The shank is the visible difference; the important ones are inside. An SDS drill delivers blow energy measured in joules, tens of times what a combi produces, and a bit made for the smaller machine is not built to receive that.
Step by step
- Compare the shanks.Round and smooth on a masonry bit, gripped by chuck jaws. Grooved and slotted on an SDS bit, locked by balls and driven by ribs, and deliberately free to slide a few millimetres.
- Compare the flutes.SDS bits have deeper, more open flutes because they cut faster and produce dust far quicker. A shallow-fluted bit driven hard packs its flutes, and a packed flute stops cutting instantly.
- Compare the tips.Both are tungsten carbide, but SDS tips are larger, more robustly brazed and often ground into a four-cutter or cross shape that survives hitting reinforcement and aggregate. A combi bit's tip can be knocked off by an SDS.
- Do not put an SDS bit in a chuck.The jaws have nothing to bite on, the shank is hardened, and the bit is designed to slide. It will spin, damage the jaws and can be ejected.
- Do not expect a masonry bit in an SDS adaptor to work well.With hammer off it drills nothing useful in masonry. With hammer on the percussion cannot reach the bit through the adaptor. Either way you have thrown away the tool's advantage.
- Match the bit length to the job.SDS bits come in long lengths for through-wall work; combi masonry bits mostly do not, and a long thin combi bit flexes badly. If you need to go through a cavity wall, that is an SDS length in an SDS tool.
- Check for SDS-plus against SDS-max.SDS-plus is the domestic and light trade format. SDS-max is larger, for heavy breakers and big cores. They do not interchange, and the packaging states which.
- Retire a masonry bit by its tip, not its length.A carbide tip that has gone rounded or has a chipped corner stops cutting and starts polishing. That is when the hole takes ten times as long and people conclude the wall is concrete.
Tips
- Masonry bits are sized to the wall plug, so the size on the bit matters more than on any other bit type. Check the plug packaging rather than guessing.
- Withdraw the bit fully every 20 or 30mm in deep holes to clear dust. This is more important with a shallow-fluted combi bit than with an SDS.
- A carbide tip is brittle. Dropping a masonry bit onto a hard floor tip-first can chip it invisibly, and it will never cut properly again.
Questions people ask
Can I use SDS bits in a combi drill?
No. The chuck cannot hold the shank securely and the bit is designed to slide. Buy round-shank masonry bits for a combi.
Why does my SDS bit make a much bigger hole than the size on it?
Usually because the tool is being levered around while drilling, or the bit is bent. A blunt tip also enlarges the hole as it grinds rather than chips.
Are TCT and masonry bits the same thing?
Masonry bits are one kind of TCT — tungsten carbide tipped — bit. The label TCT also appears on saw blades and hole saws, where it means the same material and a different tool.