(Left) Prototype Zehna pistol. Front plate extends below front of frame (similar to Mauser Pocket Pistol) and has a short round peg beneath the recoil spring guide rod. Wide top groove.
(2nd from Left) Type I. Front plate extends upward, has a round peg that fits into a hole just beneath the barrel, and has cutouts on the side for the fingernails to grasp. Wide top groove
(3rd from Left) Type II. Front plate has a tongue shaped projection at the top that fits into a transverse slot beneath the barrel, and has serrations at top and bottom. Narrow top groove.
(Right) Type III. Front plate is eliminated altogether. Narrow top groove.
by Ed Buffaloe.