In article , Jeff Wisnia says...

Check the thread form drawings in Machinery's Handbook and you'll see
that the crests of male NPT threads are truncated, which creates the
well known "spiral leak path" requiring some kind of "pipe dope" to plug it.

Yep. And I saw a parker representative demonstrate that yes,
the goop in the spiral leak path does indeed extrude out at
extreme pressures - *before* a swagelock fitting will let loose.

Jim


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