Post By gnorbury
Converting NPT tap to NPTS
I need two 1/2 inch brass elbows with one leg NPT and one leg NPTS. Tried Google and McMaster and cannot find any.
McMaster has a 1/2 NPTS tap, but it is over $50+. This is way too much for just two threads.
I have surplus NPT taps. Can anyone see a problem with picking up the major diameter of NPTS on the NPT tap and just
grinding out all of the larger threads?
This is for a fuel tank vent. It needs to be liquid tight, but almost no pressure.
EDIT: Sorry, I think the initials are wrong. One leg needs to be tapered, the other straight.
NPTS will not hold liquid or anything else tight. It is a mechanical thread.
Last edited by WHHJR; 06-20-2012 at 06:37 PM.
I presume by "NPTS" the OP means straight or NPS threads. This being the case, you obtain a liquid-tight seal by using a fitting that has a flange and crush washer, or an o-ring.
Originally Posted by WHHJR
For $50 it is probably a import. I know 1/4 straight taps in that size are about $100.
Originally Posted by mm
I think you are a fool if you are playing games with pipe threads on a gas tank to save a few bucks.
Besides if you try to convert a fitting from tapered to straight the profile of the finished thread will
not be all straight. Get a 3/8 fitting and enlarge to 1/2 is the way to go, if you can't find any 1/2 elbows.
Victor has the taps. Some USA made, some import, but they will tell you.
1000's of taps - inch, metric, special, pipe
I've bought from them and been satisfied with their service.
Just a pressure vent? Let's out fumes in the hot sun? Must be, but why did they bother to design a part that requires 2 tools? Wouldn't hurt to make both tapered even if not required.
Anyways, these guys probably have the tap you need in some quality or other.
You want a bulkhead fitting. straight threads on one side and pipe on the other. Or straight to AN and go right to the hose. Or weld a bung in the tank and use pipe thread into the tank.
Just skip the bulkhead fitting and weld a pipe stub to your tank. Use a union or a pipe fitting to connect to the stub.
A male npt and npts will both screw into and seal in a npt female fitting.(neather will seal in a npts female)
A npts tap is for producing a nut (used in a bulkhead situation)
If it leaks tap the fitting with a nptf (if you have enough room)
mcmaster has nps elbows. look for nps, not npts as mentioned above. not sure why but people assume npt to stand for nat'l pipe thread, when it stands for nat'l pipe taper. nps stands for nat'l pipe straight.
you can also cut and weld fittings. i worked in a hydraulic hose shop and we used to do this all the time when we couldnt find the adapter we needed. just two of what we did need in half and weld them together.
I would have failed Machine shop in Gr. 10 if I refered to a taper as a thread. ---Trevor