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Ron,
The fitting I pulled out has an NPT 1/4-18 on the block side and what
appears to be a BSPP 1/4" on the line side. I bought a 1/4-18 tap and
die from NAPA today and did some checking. The die fit on the fitting
very easily and was still easy all the way to the base. The tap actually
went into the block quite easily and then tightened towards the end of
the tap. So the conclusion was there is nothing wrong with the fitting
or the threads in the block. However, when I inserted the fitting into
the block, it would progress about 4 threads before it stopped. I took
it out and inserted a 1/4" MIP brass fitting into the block and it
tightened down after about 7 threads. I pulled it out and measured the
thread diameter at the point where it stopped. They were at about the
same diameter reading but were at different depths on the fittings. It
turns out my original fittings has a different taper than the brass
fitting as well as being much thicker at the base end. I am thinking
someone may have used an NPTF thread which gets crushed at insertion, is
very hard to extract, and cannot be used again. This would address all
of the symptoms I experienced while removing the fitting and trying to
reinsert it back into the block. I am going to order a new fitting and
see what happens.
Thanks for doing additional research on it for me.
Cheers, Terry
On 7/4/21, 11:02 AM, Ron Fraser wrote:
>
> Terry
>
> I did some more digging and I find there is a difference in the number
> of threads per inch.
>
> NPTF
>
> 1/8â?? 27 threads/ inch
>
> ¼â?? 18
>
> BSPT
>
> 1/8â?? 28 threads/ inch
>
> ¼â?? 19
>
> So these 2 systems have threads that are not totally compatible or
> interchangeable.
>
> I believe the tubing end of the adaptor is parallel thread.
>
> The threads per inch is the same for either system tapered or parallel.
>
> I would suggest measuring the part accurately is the only way to know
> for sure.
>
> Ron Fraser
>
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Ron, <br>
<br>
 The fitting I pulled out has an NPT 1/4-18 on the block side and
what appears to be a BSPP 1/4" on the line side. I bought a 1/4-18
tap and die from NAPA today and did some checking. The die fit on
the fitting very easily and was still easy all the way to the base.
The tap actually went into the block quite easily and then tightened
towards the end of the tap. So the conclusion was there is nothing
wrong with the fitting or the threads in the block. However, when I
inserted the fitting into the block, it would progress about 4
threads before it stopped. I took it out and inserted a 1/4" MIP
brass fitting into the block and it tightened down after about 7
threads. I pulled it out and measured the thread diameter at the
point where it stopped. They were at about the same diameter reading
but were at different depths on the fittings. It turns out my
original fittings has a different taper than the brass fitting as
well as being much thicker at the base end. I am thinking someone
may have used an NPTF thread which gets crushed at insertion, is
very hard to extract, and cannot be used again. This would address
all of the symptoms I experienced while removing the fitting and
trying to reinsert it back into the block. I am going to order a new
fitting and see what happens.<br>
 Thanks for doing additional research on it for me.<br>
<br>
Cheers, Terry<br>
<br>
<br>
<div class="moz-cite-prefix">On 7/4/21, 11:02 AM, Ron Fraser wrote:<br>
</div>
<blockquote cite="mid:000e01d770ed$f377e540$da67afc0$@bluefrog.com"
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<p class="MsoNormal"><span
style="color:windowtext">Terry<o:p></o:p></span></p>
<p class="MsoNormal"><span
style="color:windowtext">Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â
I did some more digging and I find there is a difference in
the number of threads per inch.<o:p></o:p></span></p>
<p class="MsoNormal"><span
style="color:windowtext"><o:p>Â </o:p></span></p>
<p class="MsoNormal"><span
style="color:windowtext">NPTF<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:windowtext">1/8â??     Â
27 threads/ inch<o:p></o:p></span></p>
<p class="MsoNormal"><span
style="color:windowtext">¼â??         Â
18<o:p></o:p></span></p>
<p class="MsoNormal"><span
style="color:windowtext"><o:p>Â </o:p></span></p>
<p class="MsoNormal"><span
style="color:windowtext">BSPT<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:windowtext">1/8â??     Â
28 threads/ inch<o:p></o:p></span></p>
<p class="MsoNormal"><span
style="color:windowtext">¼â??         Â
19<o:p></o:p></span></p>
<p class="MsoNormal"><span
style="color:windowtext"><o:p>Â </o:p></span></p>
<p class="MsoNormal"><span style="color:windowtext">So these 2
systems have threads that are not totally compatible or
interchangeable. <o:p></o:p></span></p>
<p class="MsoNormal"><span
style="color:windowtext"><o:p>Â </o:p></span></p>
<p class="MsoNormal"><span style="color:windowtext">I believe
the tubing end of the adaptor is parallel
thread.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:windowtext">The threads
per inch is the same for either system tapered or
parallel.<o:p></o:p></span></p>
<p class="MsoNormal"><span
style="color:windowtext"><o:p>Â </o:p></span></p>
<p class="MsoNormal"><span style="color:windowtext">I would
suggest measuring the part accurately is the only way to
know for sure.<o:p></o:p></span></p>
<p class="MsoNormal"><span
style="color:windowtext"><o:p>Â </o:p></span></p>
<p class="MsoNormal"><span style="color:windowtext">Ron
Fraser<o:p></o:p></span></p>
<p class="MsoNormal"><span
style="color:windowtext"><o:p>Â </o:p></span></p>
<p class="MsoNormal"><span
style="color:windowtext"><o:p>Â </o:p></span></p>
</div>
</blockquote>
<br>
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