Should be 5/16" steel tubing shouldn't it?
One end with a flare that has the nut captive to the tube.
The hose end should have a bead or bubble.
That's more difficult to find. Not sure if any of the Imperial flare kits can do that.
Parker tube beading tool. View attachment 1715783656
Not sure what type of place would have one.
I ending up buying a used one.
Double flare on one end and bubble flare on the other. Double Bubble. Only you old guys will know what i am talking about. I sold a lot of combination kits that had dies to do both.