I assume this double-sided 13 was once part of a carnival game or something like that--or perhaps it marked an especially challenging obstacle on some sort of course, of the sort where balls, or people, disappeared! I personally find the number 13 lucky and am sure this one is--and a great looking one too, which one could hang somewhere to look bad luck in the face.
9" in diameter, with great surface wear. Steel I believe, with a nice weight and a hole at top for hanging.