In article ,
says...
On Mon, 13 Oct 2003 20:22:56 -0400, Ned Simmons wrote:
Oh, come on, Ed. What's so different about pipe threads
that they don't "exploit the strength of the material"? The
sharp thread form likely causes some stress concentrations,
but other than that, I don't see much difference.

They're *tapered*. That means you don't have full depth threads
engaging full depth threads at any point in the joint. Machinery's
Handbook says that only NPS threads should be used for axial
loading.


The major, minor, and pitch diameters all follow the same
taper, so the thread form remains constant throughout the
length of engagement.

You must have a different MH than I do - mine (22nd ed)
says,

"While external and internal taper pipe threads are
recommended for pipe joints in PRACTICALLY EVERY SERVICE,
there are mechanical joints where straight pipe threads are
used to advantage."

And from Kent's Mechanical Engineer's Handbook (11th ed),

"Taper male and female threads are recommended for threaded
joints for ANY SERVICE. ... Straight male threads are
applicable only to special purposes, as long screws and
tank nipples."

My emphasis added in both cases.

Ned Simmons