Plastic Insert for 1/4'' Swivel Nuts
Use this insert for 1/4" Flare fitting applications where you
would have metal on metal action.
i.e. connecting a 1/4" swivel nut to a brass 1/4" MFL on your regulator.
You shouldn't need one of these to connect a swivel nut to a gas or
liquid disconnect with the MFL fitting, because those are usually plasic