A short length of rack teeth on the base of the movable jaw engages rack teeth on the face of the main shank. A set screw secures the adjustment. The rocking portion of the movable jaw has an elongated slot to allow for rocking motion. A spring attached to the base of the movable jaw provides pressure to hold the rocking jaw either "open" or "closed" as it presses against the rocking jaw just in line with or slightly "below" the pivot pin.
A known example appears to be at least partially hand forged, and is stamped with the patent date.