The mission of this key or screwdriver is to enable the person who maintains the blue gas tank to easily remove the old inner valve of the Italian blue gas tank and replace it with a new valve, or as some like to call it, the gas valve.
Also, using this screwdriver, you can open the winding screw (the side screw of the blue gas tank) and re-tighten it again (this process is repeated with you often if you are one of the people who practice filling your tank without resorting to gas shops).