Thanks to everyone who helped out on this.

The short answer seems to be that there IS a 3/4-27 thread.

The longer answer goes like this...

I took a harder look at "Machinery's Handbook" and there are more
threads than you'll ever want to deal with.

They show a 3/4-27 UNS thread and suggest that UNS not be used unless
other threads "do not meet requirements". I don't know what's so special
about this CO2 cylinder but...

It isn't metric. The closest metric pitch is .09 and 27 TPI comes out as
..094
( 25.4/27) And 27 is the correct # (Using thread gauge.)

It isn't NTP. While NTP does have a 27 TPI, it's down at the 1/16" size.


Now all I have to do is find or make a 3/4-27 tap! :-)

DOC



wrote in message
. ..
it is 1/2 NPS (Nation pipe straight ) i have bp
"DOC" wrote in message
...
I recently picked up some CO2 cylinders which I want to use as the
power source for small combat robots. Think flipper, hammer...

Couple pics he
http://www3.sympatico.ca/doc/co21.jpg
http://www3.sympatico.ca/doc/co22.jpg

I make the external thread out to be 3/4-27. That's something
I've never heard of! Proprietary?

The things are made by the Walter Kidde Company Limited and, although
unused, say "Made in England 1958", "Part No. WKA25533"

Can't find anything on the web.

Any idea what kind of fitting this is?

Tanks,
DOC

Small pun intended! :-)