Found in a harvested cornfield that was once the grounds for a schoolhouse (approx 1910-1955). The back shank has a hex nut on it, and it appears the shank has threads on it.
I agree! The WW1 era collar brass did not have the smooth background (it had fine lines engraved). The hex nut is not original to the piece but was probably a soldier making due with what he had.
Thanks both of you. After I read your reply I happened to see a gilded version being worn on the uniform (collar) of an actor portraying a soldier in Stephen King's "The Mist".