DIYbanter - View Single Post - Damn - 5/16-32 TPI Is Not 8x0.75mm Ooffah!

David Billington · **Damn - 5/16-32 TPI Is Not 8x0.75mm Ooffah!**

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.