2-1/8” with metal back and bar pin. No maker name but manufacturing style indicates mid-1960s. Art shows cross-eyed Batman cartoon with text “Bat The Bison/’Hate State.’” Upper right has one tiny raised bump caused in the making by the reverse bar pin. Button is most likely from the University of North Dakota with the slogan in opposition to North Dakota State. Slightest bit of tan tone on the left side but barely perceptible in most light conditions. Very limited and the only example we’ve seen.