What is this regulator part

[MountainManJoe]

I was washing this CO2 regulator and brass piece fell on the floor. I can't figure out where it goes. Any ideas?

 

[day_trippr]

You would use that insert to retain the original square O-ring used on that regulator stem.
It's not used with the much thicker nylon gasket, which is fine...

Cheers!

 

[MountainManJoe]

I've never seen a square o-ring.
Anyway, it seemed to fit nicely between the regulator output and the hose barb adapter so I put it there. Seems to work.

 

[mac_1103]

"Square" o-ring actually means flat o-ring. As opposed to round. Even though they're both circles.