Thats a co2/argon fitting. I had a similar regulator that I used in the beginning but I had to buy an adapter to get it to screw into the co2 tank. That regulator has a flow guage on the secondary side which really doesn't tell you how much pressure is on the output side. It works by forcing gas thru a predetermined orifice size and the "flow guage" is really just a recalibrated pressure guage to show flow thru that particular orifice. If you remove the orifice or drill it out, the flow readings on that guage don't apply. IMO, you should return that thing before you have a $29 paperweight. :lol:
FILSTAR Pimp #2
75 gal heavily planted,50/50 Black beauty,Eco-complete substrate, Pressurised CO2 with solenoid, ph controller, AB Reactor 1000, 330 watts 9325K GE PC lighting,Ehiem Liquidoser, 2-Filstar xp3 canisters.