Stealth Pilot wrote:
On Fri, 11 Jan 2008 21:28:50 -0600, "Don Young"
wrote:


Going through some old taps I found a tap marked 1/4"-18. I know that is the
designation for a standard NPT tap but this tap is actually 1/4" in
diameter. Looks like a 1/4"-20 with coarser threads. Does anyone know of an
application for such a thread? I suspect it might have been made mistakenly

from a list of sizes which included the pipe thread. No manufacturer

identification and appears to be a cheap import quality.

Don Young



a 1/4 x 18 straight thread is NPSF (straight) DRYSEAL ...whatever that
means in english. it is a pipe thread.

in a taper that thread would be NPTF (taper) DRYSEAL.


Stealth Pilot


The way I learned it the "F" stood for "fuel". Things like gasoline
would disolve many of the old dopes used to seal NPT threads and allow a
"spiral leak" along the threads.

The male and female tapered dryseal thread forms are designed to make a
liquid tight metal to metal seal when tightened.

I've never heard of an NPSF (straight) dryseal thread and it's sort of
hard to see how it could work, nor did Google help me find one.

Jeff

--
Jeffry Wisnia
(W1BSV + Brass Rat '57 EE)
The speed of light is 1.98*10^14 fathoms per fortnight.