Originally Posted by Crabman
... well I`ve never seen one leak yet. ......
Nor have I.
To be clear, I was just trying to provide the information for a brass secondary plug as requested. Personally I wouldn't worry.
The new propane valves are extremely reliable. That said, so were the old style valves. The newer Acme style design does away with the confusing and harder to use (for the general public) left hand fine thread on the connection. The Overfill Prevention Device OPD came after the Acme style valve was introduced. As was mentioned, the older Acme valves do not have the three corner valve handwheel (knob) design and cannot legally be refilled.
A quick search found this link for anyone interested in more information.
There are many specific compressed gas bottle connections in the CGA Compressed Gas Association standards. The left hand thread is reserved for flammable gas. The Acme style connector was a method around that left hand thread issue. That said, they haven't eliminated the ability to be able to use the left hand thread connector on Acme style valves. I doubt that they ever will eliminate it as that connection design remains a standard.