Inverted flare adapter.
Some of the older LP dual staged regulators Coleman and Fleetwood used had a 5/16th input for the acme nut hose fitting. This adapter allows you to use today's 1/4 inch acme nut hoses with your original regulator. Consider upgrading to a new style auto change over regulator found here.
1/4 inch female inverter flare X 1/4 inch MPT.
Part number 4508132