Forgive me if this is the wrong place to post this. It is not a gun part but does go to a 37mm Flak Gun. Is that "gun related" enough?
I used to know more about this, but it has been sitting on a shelf in my gun room for a long time now so I have forgotten the details. I seem to remember that these had reticules that were specific to the task at hand. Tank reticule?
Anyway, just one of those oddities I had laying around.