Ban Liang ("Half an ounce"), no rims / Blank, no rims. 18mm, 0.38 grams. Hartill #7.13; Gratzer/Fishman "The First Round Coins of China" #13.1. 

Nice high quality example.

A Chinese ounce (liang) weighs about 16 grams. The earliest "Ban Liangs" weighed half that much - 8 grams, but the later pieces, like this one, weighed much less. In the fourth year of his reign (ca.199 BC), Emperor Gaozu issued an edict allowing private casting of small coins called elm-seed (yujia) Ban Liangs, as the government was not casting coins and there was an acute coinage shortage. The tiny "elm-seed" coins were cast until 186 BC, causing immense inflation when they were banned and large ban liangs were re-introduced.

This coin is unconditionally guaranteed to be authentic