Tools Used to Create an Internal Screw Thread in Materials

Written by wilhelm schnotz
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Tools Used to Create an Internal Screw Thread in Materials
To cut threading like inside a nut, you need a tap. (nut image by Greg Pickens from

Whether you're faced with a piece of material that needs to be able to accept bolts, or cleaning up stripped or corroded threads in an existing hole, you'll need a tap and die set. Both taps and dies are used to add threads to metal and other hard materials; dies cut threads on male pieces, such as screws and bolts; while taps add threads inside a female coupling, such as the inside of a bolt. Depending upon what sort of hole you need to thread, you have three main types of taps from which to choose. Some jobs will require you to use all three in sequence.

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Taper Taps

Taper taps are pointed taps whose narrow edge makes the first stages of tap cutting easier, although you still may need to drill a pilot hole before you start tapping the hole. Taper taps cut with more threads than plug or bottom taps, usually between eight and 10 depending upon the size of the hole and the thread pitch. With a longer cutting edge, they're slightly easier to turn and cut than the other two styles, and their point makes them easier to get started in hard surfaces.

Plug Taps

Also known as intermediate taps, plug taps feature fewer cutting threads than taper taps (four) and a broader, almost straight, tip. With its thread-cutting chamfers close to its tip, plug taps are perfect for cutting threads in a closed-bottom hole when you don't need threads all the way to the bottom. Many handymen prefer using plug taps when tapping a hole that's open on both ends, as plug taps offer a combination of cutting edge and point control.

Bottom Taps

If you need to tap a closed-bottom hole with a precision-drilled depth and need threads to reach the bottom, you'll need to finish the job with a bottom tap. Because plug taps' chamfers don't begin at their tip, they don't cut threads to the bottom of their depth, bottoming out with a couple of extra threads left uncut. Bottom taps' one or two threads extend from their tip to allow you to cut threading to the bottom of the hole.

Pipe Taps

Larger taps are available specifically to cut threads in pipe. Usually available for purchase individually, you'll need to match the pipe diameter to the tap you need to use. Pipe taps are particularly helpful to rethread stripped or corroded fittings in plumbing repair work.

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