"jim rozen" wrote in message
...
In article , Ed Huntress
says...

You probably could approximate the strength if you calculated the
strength
of three straight threads, more or less, of the same size in the same
material.

Why three? The best way would be to use the smallest
wall section.

It's stronger than that, Jim. Three is a guess, but that's the range over
which there is a roughly balanced wall section on both sides of the joint.
Where the wall section is thinnest is at the ends; neither end is the
determinant of strength.

And the sharp threads do indeed reduce
the strength.

Oh, I wouldn't dispute that. It's just that it isn't necessary to show that
the joint is weaker than one with parallel threads. And it's always
problematic because it depends on the threading tool that cuts the thread.
The standard is one thing; actual strength is another, in other words.

In fact, I just took a look, and there are ANSI, ISO, and JIS standards for
mechanical strength of tapered threads -- apparently. I say "apparently"
because they're mentioned in the abstracts, but it costs money to get the
full standards, and I'm not buying. g

It should be noted that parallel pipe thread standards say "mechanical
joints," and tapered pipe threads say "sealing joints," but both mention
mechanical strength.

Ed Huntress