"Stealth Pilot" wrote in message
...
On Mon, 14 Jan 2008 05:56:18 +1300, Tom
wrote:

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

I hope you read you pilot notes with greater concentration than you did
the
original post? :-)

Tom

why what's the problem? I read the details from my mullins thread wall
chart. it lists the 18 pitch threads exactly as quoted.

the post answers the last two sentences of the question.
a. what's it used for? - pipe thread.
b. his suspicion that it was a mistake is probably wrong since there
is a listed application for the thread size.

pilot notes .....pilot notes??? now what are they? a description of
the machining standards for slocumbe drills?

Stealth :-) Pilot

You missed the fact that this thread in question is 1/4" diameter. It
is *not* a pipe thread. It is a non-standard 1/4" tap.

Harold