cutting npt threads

Srtraight is what it takes.

The tap takes care of the taper.

It's the thread depth which "tapers", not the hole.

HTH,

Jeff

They tell me that there are tapered reamers for this but I've never used one. Randy Replogle

I have threaded internal NPT threads both on straight and on tapered holes. You remove less metal with a hole that is tapered, so you wear your tap less and also it's easier to turn the tap. But on 16mm aluminum (britspelled "-ium") it wouldn't be that different. If I were doing this, I'd use kerosene for cutting fluid.

GWE

Randy Replogle wrote:

Both the major and minor diameters taper on my NPT taps, Jeff.

Argh! I'll fall on my sword. I didn't say what I meant.

I was remembering having worked in a place where we tapped 1-1/4" and

But, Machinery's Handbook does say, "To secure the best results the hole should be reamed before tapping with a reamer having a taper of 1/4 inch per foot."

Jeff (Never too old to learn something.)