I'll try to remember to take some pics. Yes, they're just delrin DIN caps. The seal is made by the reg's o-ring pressing against the flat Delrin surface inside, in the exact same manner it seals into your tank (although without the same pressure, of course), and I'd imagine the threads offer some degree of protection as well. Drop me a PM sometime and I'll post a pic or two. They don't seem like anything special to me, just another thing cluttering the wall at my LDS. I was stunned to hear about the existence of DIN caps that don't seal... what's the point? "Dust"?