What is the difference between A clamp and din? :S
An a-clamp or yoke fitting fits over the top of the pillar valve of the dive tank and you then tighten it against the valve to make a seal over the 'air port'.
a DIN fitting actually screws into the pillar valve, the fact that it is a stronger fitting means that it can be used on 232 or 300 bar tanks whereas an a-clamp can only be used on 232 bar tanks.
many pillar valves have an insert which will allow the use of both types.