Maybe my feeler guages are old, but the three that I have include one blade that is brass, and this was always the one we used to set the air gap on fly wheel maganetos. Guess I am dating myself, but it has worked well for me, most recently I used it to set a Maytag twin off of a gas powered Matag Washing Machine. I also have a variety of weedies and chainsaws, but have converted most of mine to electronic set-ups. I will check my stash (my wife says I never throw anything away) and see if I have a coil that matches your picture.
FLATHEAD::::