Drill bit

A drill bit is a rotary cutting tool used to create round holes in material. It is mounted in a drill — hand-held or drill press — and spun at high speed while being pressed into the workpiece.

How it works

The cutting edges at the tip of the bit shear away material as the bit rotates, and the helical flutes along the shaft carry chips up and out of the hole. The point angle (typically 118° or 135° for general-purpose bits) determines how the bit enters the material: a sharper angle penetrates faster but is more prone to walking off-centre.

Common types

• Twist bit: The standard general-purpose bit with helical flutes. Available in sizes from fractions of a millimetre to over 100 mm.
• Brad-point bit: Has a sharp centre point and outer spurs for clean, accurate holes in wood.
• Forstner bit: Cuts flat-bottomed holes with clean edges, used in woodworking for hinge recesses and plug holes.
• Spade bit: A flat, paddle-shaped bit for fast, rough holes in wood. Common in electrical rough-in work.
• Step bit (unibit): A conical bit with stepped diameters, used for drilling sheet metal in multiple sizes without changing bits.
• Hole saw: A cylindrical cutter with teeth around the edge, used for large-diameter holes in wood, metal, and masonry.
• Masonry bit: Has a carbide tip designed to hammer and grind through concrete, brick, and stone.

Materials

• High-speed steel (HSS): The most common material — durable, affordable, and suitable for wood, metal, and plastic.
• Carbide-tipped: Extremely hard, used for masonry, tile, and abrasive materials. Stays sharp much longer than HSS.
• Cobalt: An HSS alloy with added cobalt for heat resistance. Used for drilling stainless steel and hard alloys.