Ok, so I have a oxy acetylene here, but some of my regulators have no gauges, just some numbers on the neck of the adjustment to indicate the pressure setting.
they are outlets threaded capped off for contents and outlet pressure gauges but I wouldn't bother fitting any to them . just buy a new pair of regulators with them already fitted . safety and cost of 4 gauges its not worth the bother
2 stage ones are supposed to be more finely regulated but I have single stage and don't have any problems regulating using a sapphire torch with no 1 to 6 blowpipes
Single stage are fine for everyday heating and cutting, two-stage are suited to welding over a long period or heavy cutting & heating less chance of flame altering once set as the cylinder pressure drops.
Thanks, one more question, oxygen output pressure 4 bar or 10 bar if you do welding and cutting? I'm going to stick with single stage regulators as I dont use it long enough to justify the cost of the multi stage ones.