Here's a picture of what I'm sure I used on our Cub when I replaced the previous owners rubber hose. I know I've used it on other similar looking carb and mixer inlets on some of our gas engines.
It's called a "Double Compression" fitting. I don't think it is available any more as it's not listed in the newer Weatherhead books. In one of the old books I have it's part Number is; 6100x5 for the 5/16 line. It's 1/2x20 thread.
If they are available or you can find old stock you can also get a male connector, if someone has done the all to familiar 1/8 pipe hose barb replacement. The number for the connector is; 6200x5.