Two Chinese characters Ban Liang ("Half an ounce"), inner and outer rim / Flat, no rims. 24mm, 2.91 grams. Gratzer/Fishman "The Early Round Coins of China" #13.109.

Very rare type in lead, probably a private issue, listed in Gratzer/Fishman as #A13.109 (rated "Very rare", with no picture available, just a rubbing).

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 reigns of Emperors Wen (180-157 BC) or Jing (157-141 BC), the date of the casting is ca.175-140 BC.

This coin is unconditionally guaranteed to be authentic