Four Chinese characters (read clockwise) - 元豊通寶 Gen Ho Tsu Ho (Japanese reading, one-dot Tsu) / Blank. 24mm, 3.57 grams. Issued 1641-1685. Hartill -; History and Guide to the Copper Cash Coinage of Japan #177.
These coins were cast in the 17th century in Nagasaki (from 1641, the only port in Japan open to trade) to facilitate trade between Japan and Vietnam. Japan was exchanging silver and copper for raw silk, sugar, spices and sandalwood. After several requests and denials, on the 14th day of the 7th month of the 2nd year of Manji (1659) the Tokugawa Shogunate gave permission to Nagasaki to cast coins, and they continued to do so until 1685. These coins are known as Nagasaki Trade Coins (長崎貿易銭Nagasaki Boeki-sen), and circulated in Vietnam along with the small coins minted locally. The trade must have been profitable for the Japanese, for it is recorded that a string of cash worth 1 liang of silver in Japan was priced at 10.5 liang in Vietnam. The inscriptions on these coins were derived from those of the Chinese Song Dynasty (960-1127), for it was stipulated that these coins should not bear the officially issued Kuanei tsuho inscription, but their style and make-up are very different to Song coins, and their square holes tend to be larger. These coins are comparatively common, and there are a number of variations within the various types. Vietnamese copies of the Gen Ho coins are also found, their style much removed from their fine Song ancestors.