Apeks 1/2 - 3/8 Adapter

[ScoobieDooo]

Hi,
I have a 1/2" to 3/8" adapter for my Apek's ATX50 to install. Is there supposed to be any kinf of O-ring on the adapter itself?

Its this adapter:

 

[Scubaroo]

Yet to see a hose connection in scuba without one.

I have a different style 1/2"->3/8" adapter in my toolbox that I no longer use - it had an o-ring on it. Try taking one off the 1/2" hose you'll be replacing? Ideally a new o-ring would be better.