If your car's gas filler is its hungry mouth, then its gas cap has to be its, um, mouth-cover? Pacifier? No, that's terrible. This analogy is terrible. The point is, interesting gas caps are rare, so ...

Editor's note: Wayne Liebhard's interest in '65-'66 Mustang dealer-installed options and accessories has resulted in one of the best collections in the world. We asked him to put his knowledge to work ...