On Sun, 06 May 2012 00:17:34 +0100, David Billington
wrote:

wrote:
On Fri, 4 May 2012 09:50:33 -0700, "Bob La Londe"
wrote:


"Doug Miller" wrote in message
. ..

"Wild_Bill" wrote in
news:HeRor.293664$5f3.191913
@en-nntp-12.dc1.easynews.com:


So I have this little spindle that I wanted to make some accessories for,
and checked the size a couple of different ways, and came to the
conclusion
that the thread is 5/16-32.

I tapped the hole with a new tap, and was ready to fit the part..
Ahh****,
no Worky.

The thread checks sure looked correct. I wondered how far off a 0.75mm
pitch
was, and it isn't 32 TPI but 33.866.

I didn't have much more than 1/2" of thread to examine, and the 32 TPI
tap
even matches the 0.75mm pitch fairly closely.


Counting the threads in 1/2" is sufficient to tell the two apart: 16 if
it's 32 tpi, 17 if it's 0.75mm
pitch.

Where ever possible I use a thread gage. If it doesn't fit cleanly that
isn't it.



I have, on occasion, re-tapped an existing hole for 1/8 pipe from 28
tpi to 27 tpi - use lots of dope!

Sounds like you re-tapped 1/8" BSPT? or BSPP?, which was adopted as the
international standard, to 1/8" NPT. Maybe a good move in the US as the
fittings are likely far easier to obtain as long as the application is
not demanding.
All kinds of oddball stuff comes to light saturday mornings. Some
useful, some just interesting.