On Thu, 08 Nov 2012 15:29:10 -0900, Bruce Gordon
wrote:

The thread is Straight Cut as opposed to NPT, which is Tapered...
HOWEVER,

I have cut 3/4" NPT Threads, using my Pipe Threader, that will work on
Marine Antennas. The trick is to have an Adjustable Die, and cut the
threads just a tad bit deeper than normal 3/4" NPT. It works well, as
long as your Pipe has enough wall thickness, to take the deeper
threading. I have used in in Alaska for years, and had no issues with
the antennas or mounts.

That sorta works because 3/4" NPT is also 14 TPI (threads per inch).
Also, pipe is measured by the inside diameter, while nut and bolt type
hardware, which includes 1"-14 antennas, is measured by the outside
diameter. The result is that 3/4" NPT and 1"-14 UNS can be made to
fit.

I've seen the results of this method of antenna mounting. If the
antenna base is heavy and strong, it will work. If it's cheap pot
metal, the tapered pipe thread will crack the base when tightened. If
the 3/4" NPT is a little on the large side, it will be supported by
only by one or two threads. Hit the antenna with anything, and the
base will peel out of the mount.

The practice of using 3/4" NPT mounting is even more of a problem with
GPS antennas, which are usually mounted on some manner of pipe. In
order to avoid having two thread standards, Trimble and other have
standardized on an odd compromise threading that works with both 1"-14
and 3/4" NPT. For example:
http://trl.trimble.com/docushare/dsweb/Get/Document-8420/Bullet-III_DS.pdf
The socket accepts either a 1"-14 straight thread (typical
marine antenna mount) or a 3/4" pipe thread.
However, to the best of my knowledge, such a thread is not used in
marine antennas.


--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558