thank you for that item A was the info i read the triggered my questions. something about 200 and 300 bar thread differences because of an EU STANDARD. osmething about not being able to do what is done inthe US I wasnot sure itf it was the tank neck thread or the reg thread or both beinf different to prevent matching 300 bar parts on a 200 bar tanks. Other than measuring the thread is there perhaps a stamp on the reg or part to show it is an EU standard part?
I don't completely understand your question. If you have the 1st stage or a good image of its DIN fitting you can simply count the threads on the fitting. I have not seen a stamp/mark for the type of DIN fitting but I have seen stamps/marks such as EN250, EN250A...these marks mean the 1st stage is certified to meet certain performance standards in the EU. Here is a website that explains what the markings mean:
What is EN250?
If you are not buying a reg specifically with the wider M26 threads designed for use with high concentrations of O2 then you really have little to worry about.
If the product info for the regulator(s) you are interested in state the 1st stage is rated upto 300 bar, the DIN fitting will have 7 threads. Here is an example cut and pasted from Aqualung's product info webpage for their COR Supreme 1st stage:
Yoke or DIN Available in yoke (3,300psi/232 bar max.) or DIN (4,350psi/300 bar max.)
Here is product info taken from a product web page regarding an Apeks Mtx-R 1st stage that indicates it can be purchased as a specific version for use with high O2 mixes that has the M26 thread diameter on the fitting:
DIN, Yoke and M26 Thread available, 300bar, 232bar and M26 300bar (O2) respectively
With the exception of tanks valves designed for M26 threaded DIN 1st stages, a 300 bar DIN 1st stage will fit on either a 300 bar DIN tank valve or a DIN tanks valve designed for a lower pressure rating. A 232 bar DIN 1st stage, while uncommon (even more so in the US), can only be properly paired with a 232 bar DIN valve.
I am not 100% sure about tanks made in North America, but I believe that HP tanks have narrower neck openings and require a valve that is threaded 7/8 UNF, whereas most currently manufactured LP tanks use 3/4 NPS threading. To my knowledge, Europe (with perhaps the UK as the exception?) has standardized on the M25x2 neck threading for both LP (232bar) and HP (300bar) tanks.
If you share what reg set you are interested in it perhaps the collective mind here could advise on the type of DIN fitting.
-Z