The two designs are nearly identical, but the 300 bar valve outlet is
deliberately deeper so the shorter 200 bar connector will not be long
enough to seat properly. This is a safety feature to prevent connecting
a low pressure device to a high pressure supply, but it works perfectly
well to use a 300 bar connector (like those found on most dive
regulators) with a 200 bar valve outlet. The 200 bar outlet can also
accept a screw-in adapter to convert the outlet to accept the standard
'yoke' style regulator fittings. It's important to understand that
the "200 bar" or "300 bar" descriptions are just slang terms that have
nothing to do with the pressure ratings of the outlets and connectors
themselves.
For details read SCUBA Valves: Regulator Fittings, 200 vs 300 Bar FAQ and Cylinder Neck Threads.
