In article , Fdmorrison says...

I'm no engineer, and only an amateur machinist.

Often amateur machinists a) have a better intuitive grasp
on the issues than 'real' engineers, b) know enough to
look stuff up when they know they *don't* know the answer,
and c) have open minds.

My problem with this is, if there is a taper-thread-induced concern with "pipe"
thread, why not disclaim its use for vertical holding whatsoever, rather than
go into guesses as to the possibilities?

That is pretty much what others have said on this thread
before. Pipe threads are not spec'd for tensile strength
but facts are this widget is already built. My two suggestions
(calculate based on the minimum wall thickness, then divide
by three to account for stress concentration, and the other
was to simply make up a joint like that, and stress to
failure) are only to encourage the fabricator to think a
bit more about his machine.

Jim

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