I had my cylinders pressure tested and re stamped at a local fire service shop that work on Co2 bottles which after 10 years need a pressure test...
I have the 2351 brass pouring jug, looks like its about 600ml
They are 1/4 whitworth, make sure you do not make them too long as they will punch through your tank when tightening Rgds Tony
Separate names with a comma.