Ford calls it a Locking Fuel Plug. It's $24.99 from the dealer, ordered it for $21.07 from Amazon with free shipping.
This should have been standard equipment, not only for security but to keep dust/debris out of the fill pipe.
https://www.amazon.com/gp/product/B001H1O688/ref=ask_ql_qh_dp_hza
This should have been standard equipment, not only for security but to keep dust/debris out of the fill pipe.
https://www.amazon.com/gp/product/B001H1O688/ref=ask_ql_qh_dp_hza