fuel line reducer

Looks like you have a 3/8" Edelbrock banjo fitting, and you want to go to 5/16" fuel line.

Looks like you have a small block ?

I would shake the Edelbrock 3/8" banjo fitting, and get the correct 318,340,360 fuel line.
5/16" pump to carb fuel line. Inexpensive, and easy to get.