Dolphin, not many people would have noticed that the later PST HP tanks (sold as generic or 'Aquaaire') have a slightly thicker neck than earlier versions, which means the majority of those manufactured. My compliments.
There is no difference in the quality or safety of the two types of 7/8-14 threaded neck. However, it is usually a good idea to have a strong neck to control expansion in the throat area of the tank. One factoid, if you look carefully you will see that PST tapered the thicker neck slightly to match up the slender DIN valve body.
The PST HP tank is a marvelous accomplishment. However, I understand that PST is now making a HP tank with a slightly lower rating, 3442 psi and the neck is no longer 7/8 NMT but standard 3/4 NSPT, like on aluminum tanks.
Edit: Whoops! After rereading your message I realize that your question was much more elementary than I took it to be. I threw the ball clean over your head. Yep, those funny looking tanks with the little necks were sold under differing brand names, as 'hacker' and others said. They're good tanks. They have the small neck to comply with some obscure European reg that says that HP tanks must have unique neck size to prevent fitting of LP valves borrowed from the large neck tanks.
Pesky
