Okay, I am about to switch to doubles and take all the courses. Question is I have an Apexs 1st stage that has a yolk valve. It's fitting is for regular (single tank) dives, usually. But when using doubles with a manifold you usually use Din fittings. (Please correct me if I am wrong). Am I screwed and unable to use this 1st stage. (I know I will need two of each - 1st & 2nd stages) I just would like to already have one 1st & 2nd set ready.