Which way is the nylon washer between the CO2 regulator and tank supposed to face?

[thehopbandit]

Between the CO2 regulator and CO2 tank goes the round nylon washer. It has a smaller side that "pokes out" and a larger flat side. Which side is supposed to face the regulator and which side is supposed to face the tank?

Both sides have grooves and they both seem to fit either way.

Any idea? What do you do?

 

[day_trippr]

I'd be surprised if it matters, I've always just stuffed 'em in the coupler without checking which way was which and never have had a leak there...

Cheers!