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Greenfield Threading Tech Tip: Pipe Taps… How Deep to Thread?

Greenfield Taps with Cutting Tools Chicago aka General Cutting Tools answers the question: Do you know how deep to run a pipe tap into a drilled hole before it stops? In other words, do you know when the pipe thread is either too small to accept the L-1 thread plug gage, or too large to be flush with the surface of the hole being tapped within ± 1 turn on the gage?

Pipe threads are sized differently than standard straight threads. They are based on the basic size  at the top of the threaded hole produced by the pipe tap. The basic size, commonly called the 12-thread count, occurs approximately 12 threads from the front of the taper pipe tap. This means you can run any standard projection pipe tap into a drilled hole approximately 12 threads from the front of the tap, which should be the approximate basic size for that pipe.

General purpose pipe taps are appropriate for threading a wide variety of materials, both ferrous and non-ferrous.

Ground thread pipe taps are standard in American Standard Pipe Form (NPT) and American Standard Dryseal Pipe Form (NPFT). NPT threads require the use of a sealer, like Teflon® tape or pipe compound. Dryseal taps are used to tap fittings which will give a pressure-tight joint without the use of a sealer.

The nominal size of a pipe tap is that of the pipe fitting to be tapped, not the actual size of the tap. The thread tapers 3/4″ per foot.

All pipe taps are furnished with 2 1/2 to 3 1/2 thread chamfer.

Short projection pipe taps are made with a projection shorter than standard for taper pipe tapping where the depth of tapping is limited.

Special short projection taper pipe taps can be furnished with American National Standard Taper Pipe thread (ANPT), or Dryseal American National Standard Taper Pipe thread (NPTF, PTF-SAE Short, or PTF-SPL Extra Short).

For information on short projection pipe taps and hole preparation for NPT, NPTF, and ANPT internal pipe threads, consult Greenfield’s Technical Bulletins.

Special short projection pipe taps and left hand pipe taps are available through Lightning’ Service.

Contact General Cutting Tools, your authorized Greenfield Tap and Die distributor for more information.

We ship to Illinois, Iowa, Indiana, Wisconsin, Michigan, Minnesota and the reset of the US.

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