Here's a different kind of fixed blade -
An Aqua-Craft Pro-Bar. Used by divers for taking abalone. A very unique tool.
The large, flat bar is used to pry the abalone loose from its rock. It was rounded and blunt to prevent damaging an illegal to keep abalone.
After you identify the variety of abalone, you would then measure the long dimension of the shell to see if the abalone was legal to keep.
Many ab-irons were simple flat bars with some marks on it to measure from the tip of the blade. The problem with that was it was easy to make a mistake. Big time fine if caught with undersized abalones.
If your abalone would not fit between the tines it was legal to keep. Black abalone needed to be at least 5 inches long. Green, pink and white abalone had to be at least 6 inches long. Reds had to be 7 inches.
The tool is capable of measuring lobster and clams as well. The pommel tines are for lobsters. The black abalone tines are also the same as for Northern clams at 5 inches. A separate set of 4-1/2 tines inside the GPW tines is for southern clams.