see here. If you really want to get technical though, some of the coins on that page are hemiobols. At any rate, my example is the smallest I've ever come across. It seems that hemiobols are the most common of the type, obols less so, diobols even less so. So, you need a microscope to enjoy it, but what great centering and surfaces on this fly-speck! I had to jump on it. MYSIA, Kyzikos. Circa 450-400 BC. AR Tetartemorion. 0.20 gr. – 7.5 mm. O:\ Forepart of boar left; tunny to right. R:\ Head of roaring lion left within incuse square. Von Fritze II 10; SNG France 373.