Why bit shape matters
A drill only spins the bit. The shape of the bit decides how it starts a hole, how it clears waste, how clean the edges are and how much heat it builds up. Two bits of the same diameter can behave very differently in the same board, and the wrong one may wander, burn, tear the surface or simply stall.
Most bits can be sorted into a handful of families. Learning to recognize them by the tip, the grooves (called flutes) and the shank is more useful than memorizing names.
Twist bits
The twist bit is the general-purpose bit most people picture. Two spiral flutes carry chips up and out of the hole, and a pointed tip with two cutting lips does the work. Twist bits are made for metal first, but they are also used in wood, plastic and many other materials.
The tip angle varies. A shallower point often suits softer materials, while a steeper or split-point tip tends to start more easily without skating on hard, smooth metal. Because the point is not very sharp at the very center, twist bits can wander at the start of a hole in wood. A small punch dimple in metal, or a starter mark and pilot holes in wood, help keep the bit where you want it.
Brad-point bits
A brad-point bit has a sharp center spur and two raised outer spurs. The center spur locates the bit exactly where you aim it, and the outer spurs score the wood fibers before the cutting lips lift them out. The result is typically a cleaner hole with less splintering at the entry.
These bits are designed for wood and wood-based panels. They are a common choice for dowel holes, hardware holes and anywhere the look of the hole matters. They are not meant for metal, and the delicate spurs can be damaged if you drill into a hidden nail or screw.
Spade bits
A spade bit is a flat blade with a pointed center and two cutting corners. It removes a lot of wood quickly and is inexpensive to make in large diameters, which is why it is popular for rough work such as running cable or pipe through framing.
The trade-off is a rougher hole, with more tearout where the bit exits. Spade bits also work best at higher speed in wood and can grab if you push too hard. Backing the workpiece with scrap or drilling from both sides reduces the splintering.
Auger bits
An auger bit has a threaded screw tip, a wide spiral and often a pair of cutting spurs. The screw tip pulls the bit into the wood, so it feeds itself with little downward pressure. The deep spiral clears chips well, which makes augers suited to deep holes in timber and beams.
Because the bit pulls itself forward, it can grab hard in a powerful drill. Use a firm two-handed grip and a tool with a side handle, and be ready for the drill to try to twist. Many people also prefer to use a slower speed setting for these bits, but check what your tool’s manual says.
Forstner bits
A Forstner bit cuts a flat-bottomed, clean-walled hole with a rim that guides the cut. It is the usual answer when you need a shallow, precise pocket, such as for concealed hinges, or a hole that overlaps another. Forstner bits generally work best in a drill press, where the speed and the depth are easier to control, although smaller ones can be used in a hand drill with care.
Hole saws and step bits
A hole saw is a cylindrical blade that cuts only the rim of a large hole and leaves a plug in the center. It makes holes much larger than a normal bit can, in wood, drywall or thin metal depending on the saw. A step drill bit has a stepped cone shape that enlarges a hole in thin sheet metal one size at a time and tends to leave a neat edge.
Masonry bits
Masonry bits have a hard carbide tip brazed to a steel body. They pound and grind rather than slice, and the wide flutes clear dust. They are meant for brick, block and concrete, usually with a drill that has a hammer function. For larger or repeated work in concrete, hammer drilling masonry with a dedicated rotary hammer is easier on both the tool and the user. Always wear safety glasses and a dust mask, because masonry dust is harmful to breathe.
Countersink and specialty bits
A countersink bit cuts a conical recess so a screw head sits flush, which is the heart of countersinking screws in furniture and cabinetry. Combination bits drill the pilot hole and the countersink in one pass. Specialty bits also exist for glass and tile, plug cutting and drilling in very hard materials, usually with diamond or carbide cutting edges. Check the packaging to see what material a specialty bit is designed for, because using it on something else can ruin it.
A simple way to choose
- Name the material: wood, metal, masonry, tile or plastic.
- Decide how clean and how precise the hole needs to be.
- Pick the size and depth, which the other guides in this cluster cover in detail.
- Match the shank to your drill chucks (round, hex and SDS shanks are not interchangeable), then clamp the work and put on eye protection.
When the job is unusual, the best habit is to read the manufacturer’s note on the bit and on your drill, and to unplug the tool or remove the battery before you change a bit. This is general information, not professional trade advice.