Four Chinese characters - Cho Son Tong Bo ("Choson universal currency"), inner and outer rims / Blank, inner and outer rims. 24mm, 3.64 grams. Hartill #25.73.
"Choson" was one of the old names for Korea. The coins bearing the inscription "Cho Son Tong Bo" were continuousely issued in Korea between 1423 and 1678.
This coin is unconditionally guaranteed to be authentic.