Why not just ask them to clarify what they're looking for?
I did. He sent me a link to about.com to learn about the difference between yoke and DIN tank fittings, LOL. (It takes a certain amount of finesse to negotiate meaning with people for whom English is not a first language.)
I think their concern is that Quero might follow EU rules and have M26 tank valves for EAN, in which case their 'standard' M25 regs wouldn't fit
I'm thinking this is the case as well. I didn't know that the EU had this new valve size, and the information I got here cleared that right up.
Thanks again! Not only did I learn something new (M26 valves), but I'm confident I now understand my customer's needs, and I'll do everything possible to fulfill them.