How to fit NPT fittings?

[glivingstone]

Hey Guys,
I purchased a couple of gauges to go in the truck but need a little help.
They came with 1/4 NPT fittings.
Can anyone advise as to the correct tap and drill bit to use as NPT is not commonly used over here.
Can you get a starter tap as the only one I have been able to track down over here is a tappered bottoming tap.
How does a tappered tap go into a straight hole?
Any advice will be greatly appreciated.
Cheers

[Hubert]

NPT is National Pipe Thread. It is a tappered thread meant to help seal. As the name implies its commonly used in plumbing etc. Most all the taps I have seen look like bottoming taps since its tappered it kinda looks like a starter tap also.

Since the tap is tappered it will cut heavier the deeper you tap. Normally its not a big issue use the recommended tap drill and tap to depth desired. Its just more important not to use a dull tap and always use a good tapping lube. Feel the torque required and back off if it gets too tight. It should not get too tight before proper depth with recommended drill below.

To fit gauge line depth/thread engagement just tap a little bit then test with NPT fitting. If not enough thread engagement for your liking tap a little deeper. Its easy to tap deeper to fix but if you tap too deep it can be a problem so go easy until you get a feel for it.

1/8-27 NPT = 11/32 (0.344) tap drill [~ 8.74mm]
1/4-18 NPT = 7/16 (0.438) tap drill [~11.13mm]

There are specs for gauge depth but usually its not that critical. Also, if need be you can use a slightly smaller tap drill and not tap as far and only get a little thread engagement or use a slightly larger tap drill and tap deeper for a lot of thread engagement. Only use a slightly smaller/larger tap drill a few thousands of inch. I will pick next drill on a metric/fractional inch/letter/number drill chart to compensate for material, drill, and tap condition at times.

FYI for pipe the size of the fitting is suppose to be close to the inside diameter of the pipe its for.

[moondoggie]

Good Day!

You might want to see if McMaster-Carr (http://www.mcmaster.com/)(Click in colored text) will deal with international customers or not. They have pretty near everything.

Blessings!

[Robyn]

I am decidedly currious.
What is it you need to need to drilland tap to install gauges??

Any Auto engine will have the ports already there.
Are you making some sort of manifold??

Just currious

If you cant find the tools you need they are readily available at any hardware store here and I would be happy to get them for you and mail them over.
The cost for the tools would be probably less than $20 US for good stuff and the shipping for those small items cant break the bank either.

Let me know if I can help

Robyn

[ronniejoe]

Usually, drilling and tapping is necessary to install boost and egt gages...

[glivingstone]

Thanks guys,
Found an engineers supply company that was able to supply the tap and all has gone well.
Cheers

[Robyn]

Sweeeeeeeeeeeeet
Good to hear you got it all taken care of.