NPT tread question

[Belgian1979vette]

OK, I need to tap some NPT treads. I would like to know if I would have to use a reamer first or can I just tap the drilled hole straight with the tap. If so what reamer would be a good one (size, angle etc).

Also, any good, reliable and not to expensive suppliers in the US. For these taps they charge me an arm and a leg here.

 

[big2bird]

NPT taps use a straight drill bit. The tap cuts the taper.

 

[V-Twin]

What size tap do you need and do you need it fast????

 

[Belgian1979vette]

I would certainly need a 3/8 and a 1/2, but probably a set would be cheaper in the long run.

 

[big2bird]

3/8-18NPT=37/64"tap drill
1/2-14NPT=23/32"tap drill

Sorry, I just don't know about how to solve your supply problem.
http://www.newmantools.com/tapdrill.htm

 

[Twin_Turbo]

Doesn't even have to be super precise on the drill, since it's a taper it will also thread fine if you have it a little too large. I always eyeball the drill sizes for NPT (and all the other non critical fasteners BTW)

 

[GTR1999]

If you're not used to tapping NPT threads be sure to check the fit as you go. You don't want to go too deep.