Locking lug nut

[daoust]

I was at the Eastern National Meet last week in Gettysburg, PA. In one of the 47 Fords I noticed a special nut that was used on the bracket that holds the spare tire in place in the trunk. Apparently it is some type of locking lug nut with a thick square washer. Does anyone know exactly what this nut is called and where they can be found? Any help appreciated. I'd like to find one for my car. A picture is attached.

Thank you.

David Daoust