"Eric R Snow" wrote in message
...
snip----

Since the thread is tapered the depth is controlled by
P.D. (pitch diameter). So, if the P.D. is correct, the depth muist be
correct. Pipe taps are ground this way.

.. I bet that if
a tap manufacturer were consulted they would be ablke to send you
written proof that the thread depth of a tapered pipe is controlled by
the tap cutting to the correct P.D.

Yep------and the rule of thumb is to tap until you have 5 threads (on the
tap) above the finished surface, unless you happen to have a plug gage to
check the proper depth. The rule may not be perfect, but it will always
yield a functional thread.

Harold