Can someone PLEASE explain how they come up with the name 1/8" NPT
pipe tap.

I installed my thermocouple this weekend & used it. 1/8" npt seems to be a standard for this tap. All other taps are named by thier true diameter.

The 1/8" NPT tap is NOWHERE NEAR 1/8" (.125) It is more like 11/32

 

National Pipe Thread.

It is based on the inside diameter (ID) of the actual pipe that will be threaded into it. So, adding up the wall thickness' of the actual pipe material, plus the ID.....

(I think)

 

From a pipe fitting manufacturer:
Rusty

 

???... You then would have a pipe smaller than 1/8". Its crazy to me.

Why not be like all the other taps & name it by the DIAMETER IT IS.

Back to the salt mine!

 

I agree with ya on that one.

 

I dunno....it took me a long time to figger out why the jaws of a 1/2" open end wrench weren't 1/2" apart!

Rusty

 

Oh my gosh! They've been short-changing us on our inches...

The drag race I went to the other day.....Sign said "1/8 mile tonite only"
It was a 1/4 mile track. It was tore up from an accident the previous nite.

I asked the lady in the ticket booth if the tickets were 1/2 price then...She got all flustered with me...No sense of humor

 

The ID of schedule 80 iron pipe runs really close to the nominal size. Sch.40 (the common hardware store stuff) is thinner wall. Craig

 

What he said. It is based on the diameter of the ID of the pipe that is going to be threaded into it. The size of the tap is roughly the ID of the pie, in this case 1/8 + twice the wall thickness of the pipe.

There is also a diference in the hole diameter that you drill if it is a NPT or NPTF. The NPT is a bigger hole and requires the use of thread sealent such as teflon where NPTF uses a smaller hole and has tighter tolerences and is a dry seal so theoreticly you dont need any thread sealent.

 

Also remember that the idea behind the NPT is that it is a tapered thread so it seals properly and won't leak.

You can get away with a standard size tap (can't remember exactly which one) and still screw the thermocouple in but, it will be straight walled threads and will leak.

 

Your close but read the last couple lines of what I posted above.