BOC Cylinder adapter & connector BS341 - No. 6

Here is what BOC customer service will never tell you. Most likely because they don't have a single clue of their own cylinder fitting features.
Many R134a gas cylinder supplied by BOC or Linde (but it is a quite common adapter for refrigerants HFC, Chlorine, Hydrogen Chloride ) has a bottle neck connector marked as BS341 No.6.

Although this is just a British standard but BOC doesn't mention its thread features. They either don't think it is relevant or they just missed the engineering class.

BS 341 No. 6 = BS6 = G5/8" Right Hand BSPM.  

Don't worry, RH is a standard right-handed thread just like the 80% of the threads on earth. So the BOC bottle neck has a 5/8" male outlet and most of the HVAC - air conditioning tools have the normal 1/4" flare threads. In order to connect these two you will need a 5/8" female to 1/4" SAE flare male adapter which we offer here in this listing.

GASKET IS INCLUDED WITH THE FITTING!

PS. Anyone who tries to sell this fitting by "diameter" such as 21.8mm ... that person doesn't know anything about threads or what they sell.