Yours may or may not be missing the black metal bracket.
Here are some pictures of a NOS unit I dug out tonight:
Mine doesn't have the black metal bracket and there is not a need for it,
the hole in the dash has a flat side which lines up with the flat on the
switch so it fits in perfectly. Also the wiring on mine is a little different
from yours, I don't have the blue extension wire and it hasn't been cut
off, I have two of these flashers and they are both the same.
Maybe mine are from a factory install where yours is a over the counter accessory.