Many a time when you are stuck during drilling a hole, you need a specific bit to get the job done. Let's understand the types of drill bits designed for specific purposes.

Adjustable bit: comes with an adjustable cutter to bore holes of varying sizes. Used for drilling holes for piping or wiring where a rough cut is acceptable.
Around-the-corner bit: to cut curved holes in tight corners with an angled cutting surface.
Auger Bits: designed to drill holes in wooden material. The drilling end has a screw head so that the bit can self feed.
Brad-point drills: similar to standard bits but have a sharpened point that makes it easier to start in wood. Drills cleaner holes than a spade bit.
Counterbore: a drill bit which permits a screw to be driven beneath the woods surface. The hole can then be filled with a plug.
Countersink bit: has an angled tip that's designed to form a depression for screw heads.
Drill Saw bit: Used to cut holes in metal and wood. Can enlarge existing holes.
Expansion bit: another term for adjustable bit. An expansion bit uses an adjustable cutter to bore holes of varying sizes.

Fly Cutter: used on a drill press to cut circles. The diameter of the circles can be adjusted by changing the cutter setting.
Forstner Bit: used to a create a flat bottomed hole in wood, a mortise can be formed by cutting overlapping holes. Also used to a create a segment of a hole at the edge of a board. Use only in a drill press
Glass bit: has a carbide tip for drilling through glass.
Hole saws: cuts holes from 1" to 6" in diameter, have a center bit for guiding the cutting edge of the saw.
Masonry bits: have carbide tips for drilling holes in masonry, use at speeds below 400rpm.
MultiSpur bit: drills holes large enough to run pipe or conduit through. A threaded screw in the center of the cutting circle pulls the work towards the cutting edge.
Nail Spinner: used to start finishing nails, prevents wood from splintering as it is driven in. A hammer is used to finish the job.
Reamer Bit: a tapered bit that can be used to fit into an existing hole either to enlarge it.
Rotary Files: used for the same purpose as a conventional file, great for expanding holes in metal and cleaning up rough edges.
Paint Mixers: consist of a shaft with fan type blades. Put the shaft into the paint before rotating to avoid splatter.
Plastic Bit: has a tip that prevents splintering when drilling in plastic. Drill slowly and reduce pressure as you reach the other side of you work.
Plug Cutter: can be used to cut out cylindrical shapes from wood. These small cylindrical plugs are used to cover screw heads. This bit should only be used in drill press.
Screw driving bits: used for driving screws.
Screw Pilot bit: used to drill a pilot hole, body hole and countersink all at the same time
Spade bit: has a sharpened point and used for drilling large diameter holes in wood. These bits work best at fast drilling speeds, but remember to start slowly.
Step Bit: a tapered bit with up to 13 diameters as the bit penetrates the work it drills a hole with an increasingly large diameter.
Twist drills: standard drill bits, used for drilling small diameter holes in wood and metal.
Wire Brushes: used to clean up metal, remove rust. Available as either a cup or a wheel with wire brush on the rim.
Woodscrew bit: available in a variety of sizes to match particular screw sizes. Woodscrews are used to drill a pilot hole, body hole and countersink all at the same time.

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