On Monday, December 2, 2019 at 3:46:10 PM UTC, John Rumm wrote:
Cylinders IME often have either a male threaded connection, onto which
some kind of coupling similar to that in your link can be screwed on. Or
often, the cylinder connection is just a protrusion of stainless /
copper pipe of appropriate size, onto which they expect the installer to
fix a compression fitting. If yours was previously installed and was of
the second type, you may now have a compression fitting with the
original outer compression nut and olive missing. That fitting might be
3/4" and not BSP. The outer diameter of 3/4" pipe is slightly smaller
than 22mm. That usually means that with some effort you can get a 22mm
compression fitting to mate with 3/4" pipe, but you can't get 22mm pipe
into a 3/4" compression fitting.

A photo of what you have would help...


https://www.flickr.com/photos/383551...in/dateposted/

Thanks,

Ben