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usually 1/4 or 5/16 depends on the mfg of the valve I got inserts for some din valves and they were 5/16 , but pro valves are 1/4Agree...but DIN is only safer if it's on a DIN tank
I wish all shops had those convertible tanks (I think they're also called Pro valves)? I just checked the place in Roatan that I am diving with in August and here was their response:
Most of CCV's cylinders have Pro Valves which have a removable insert that converts them from K to DIN.
Maybe I'll get a DIN and a yoke adapter, but only dive with shops that have these type tanks. There are also a few in Cozumel like this.
Any idea which size Allen wrench I'll need?