NPT tap question

notjustair · Dec 24, 2013

I have something I need to drill out and tap for 1/4 NPT threads. I've never paid much attention to taps - only if they were metric or SAE. So, do they make taps for pipe thread or do I just use standard tap threads? I've never paid any attention to whether pipe threads are anything special but they look like regular old threads.

This is what happens when I quit wrenching on machinery and have to work in the house!

Jim in Ma. · Dec 24, 2013

You need a 1/4 NPT tap, it has a taper to it.

Dusty MI · Dec 24, 2013

Yes there are pipe taps, NPT- National Pipe Taper and National Pipe Striaght.
NPS is not often seen, It's more for higher pressure.

Dusty

J. Schwiebert · Dec 24, 2013

Remember pipe threads are tapered threaded, the taps are tapered. Also there ARE straight PIPE threads which are not used in normal plumbing work. Google up a thread chart and you will see them. J.

Bob · Dec 24, 2013

.
Chart

Anonymous-0 · Dec 24, 2013

I wouldn't necessarily drill it out, as a first choice. I would use a pipe type EZ out, they are male plugs, that are "threaded" reverse, so they bite into the broken pipe, and extract the stub of broken pipe. The set I am thinking of, is 26 pieces, lettered from A-Z, and works pretty good, as long as the broken pipe is less than about 50 years old.

dr sportster · Dec 24, 2013

In the same type of pipe taps there are different sizes from different manufacturers and markings.. It might pay to measure your tap and then your fitting. Some will start to sink the fitting in too deep because they start off further into the taper of the tapered pipe thread.Others may not cut deep so your fitting only starts a couple threads. For some thing like 1/8-27 I have five taps all in a piece of wood in order of how deep they will cut. samr thing for 1/4" etc.

Steve@Advance · Dec 24, 2013

Also note, since you are working with a TAPER pipe tap, you NEVER run it in all the way as you would a regular bolt thread tap!

As a general rule, always stop with a MINIMUM of 6 threads showing above the surface of the hole you are taping.

You can then try screwing in the fitting, see how deep it goes before getting tight. You can then tap deeper if necessary. But if you go too deep...

Be careful!

PS: Check your thread pitch carefully. There are at least 2 different thread pitches (NPT and BPT) that are very similar. NPT is the most common, found on American made products, BPT found on most imported products.

J. Schwiebert · Dec 24, 2013

BPT= British Pipe Thread. It is also found on some hydraulic stuff.

J. Schwiebert · Dec 24, 2013

That is a nice chart!

retired farmer · Dec 24, 2013

Remember to also drill the hole smaller than the tap size. Bit size will be on a chart or marked on the tap. Don't remember the size bit off hand.

Wile E · Dec 25, 2013

Here is what you are to do.

1. Drill the hole with a 7/16" drill bit.

2. Tap the hole with a 1/4 NPT tap, only thread it in until you reach about 7 threads from the top of the tap. Use cutting oil while tapping.

rustred · Dec 25, 2013

would that be the same as BSP- british standard pipe? that's what I know them as for hyd. fittings.

greygoat · Dec 25, 2013

AND !, to confuse things even more, just in case
anyone is interested I have a hydraulic thread
book, by AEROQUIP, that shows that the Japanese
use BPT, British pipe thread.

NPT tap question

notjustair

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Jim in Ma.

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Dusty MI

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J. Schwiebert

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Bob

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Anonymous-0

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dr sportster

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Steve@Advance

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J. Schwiebert

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J. Schwiebert

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retired farmer

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Wile E

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rustred

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greygoat

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