304 is what I have available. 416 is nice to work with because it is magnetic and can therefore be held down on a surface grinder with a magnetic chuck. It is also easier to work. Unfortunately it is not freely available where I live.
The blade shape is a 1 arm opening or amputee design. After WW2 or WW2 (not sure) many of the men came home with an arm or hand missing. The idea is that you can hook the tip on your trouser pocket or the edge of a table to assist in opening.