A jack knife with a serpentine shape (aka Premium Jack). This pattern does NOT taper significantly from one end to the other. If there is a pronounced taper to the handles, and the blades pivot at the small end, the pattern is called a “Dogleg” or “Reverse Dogleg” depending on which way the cap end curves.

Reverse Dogleg Jack – a serpentine shape, but not a “Serpentine Jack”

Dogleg Jack – a serpentine shape, but not a “Serpentine Jack”