Pipe Threads

[oregonsteam]

I have a mini pressure gauge that the seller listed as 1/8 NTP. Is this the same as 1/8 NPT? Does this require a tapered hole for the tap? I tried to tap some scrap brass with a 1/8-27 NPT and I couldn't get the threads to "catch" Any advice?


Thanks

 

[b.lindsey]

Looks like he just transposed the letters. The proper tap drill for 1/8"-27 would be a letter "Q" drill. Hope that helps.

Bill

 

[hammers-n-nails]

i find that it helps to bore the top of the hole that is to be taped slightly larger (just enough so that you keep full threads) this helps to get the hole started and also reduces the amount of torque needed closer to the end. there is a certain taper per inch of thread(1/32"???) but i dont remember what it is that you can calculate your overbore with

 

[bearcar1]

I believe ??? the taper to be one inch per foot, for a NPT thread. I could be wrong but it is one helluva taper to thread. :big:

BC1
Jim

 

[kvom]

The recommended drill size is 11/32" BTW. I just tapped 3 such holes in brass with no problems.

 

[Stan]

The secret to cutting tapered threads is to cut the taper before you start cutting the threads.

 

[rake60]

For brass, aluminum or mild steel the "Q" drill bit is all that is
required. That hole looks pretty small compared to the 1/8" NPT
tap but that tap is not going to go full depth. If it does you will
never get a pipe fitting to tighten up in it.

Rick