Two Chinese characters Ban Liang ("Half an ounce") / Flat, no rims. 24mm, 2.40 grams. Gratzer/Fishman "The Early Round Coins of China" #13.129; BM Chinese coins (Poole) #256ff; Hartill #7.29 var. SKU T1840-50195

"Shanzi" liang describes the shape of the character "liang". It is a distinct calligraphic variety of character "liang", used mostly in the Han period.

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. These late Ban Liangs were cast during the reign of Emperor Wudi (140-87 BC), the date of the casting is ca.136-118 BC and they come from the last issue of Western Han dynasty Ban Liangs. 

This coin is unconditionally guaranteed to be authentic