There are about a dozen quick change pneumatic fitting types (Industrial, the similar V-style, Tru-Flate/automotive, ARO, ISO, Open Flow, JIC, Schrader, Lincoln, Compact, Universal, etc.) Several of them mentioned above.
If you want to sell an accessory that mates with one of these geometries, I'd be inclined to call makers and distributors to see which types have the highest market share. I'd guess "Industrial" and "Universal" but also see some of the others fairly frequently. If you're looking for a top notch maker as a distributor - same idea. Find out the market share, as well as the company's reputation for quality.