"Roger Long" wrote in message
...
Or, as another possibility, has anyone rethreaded a NPT to NPS?

I asked both a machinist friend and the shipyard and they said it
couldn't be done.

However, looking at the two half inch fittings on the desk in front of
me at this very moment, I'm damned if I can see why running a pipe die
down the first few threads of the through hull wouldn't taper it and
let it engage more than the half depth it does now.

Anybody out there got a pipe die set and want to invest $5.39 (price
of half inch bronze through hull at local store) in edifying the
boating world?

The local Lowes and Home Depots will cut threads reasonably cheaply, if you
don't have one. Unless, of course, the threads (not the taper) are
completely different in the two (which hardly seems likely, as people are
putting valves on NPS all the time).

I was thinking more along the lines of the other way - as, surely, given
that it starts that wide, the valve has enough body to support removal of
some material - taking an NPT valve and machining/tapping/whatever the entry
to NPS.

I'd think that taking material away from the TH would weaken it
unnecessarily, yielding the same end result of a small portion of the
full-depth pipe section being available to support any side loading, whereas
taking away the material in the valve shouldn't have any deleterious effect
on the strength. But then, I'm not an engineer, nor even play one on TV so
can't really comment on that.

L8R

Skip

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