Horseshoe gold is a horseshoe-shaped gold coin smelted and cast in the Western Han Dynasty, which could not appear in the Qin Dynasty. Qin unified China and the currency, and stipulated that gold was the superior currency, with the unit of "one" (20 taels); Copper is the next coin, and the unit is "half two". During the Warring States Period and the Qin Dynasty, there were half a tael of money. At first, it was the national currency, and later it was changed to the square hole round currency (). After the reunification of the Qin dynasty, the whole country carried out half a penny. Since then, the currency form of square hole round notes has been used for more than two thousand years. "Historical Records, Pingzhun Biography" quoted "Notes of Ancient and Modern Times": "Qin Qian is half a Liang, with a diameter of one inch and two cents, and weighs twelve baht." In addition, it should be a strict unit of measurement.