Four Chinese characters - TUONG PHU NGUYEN BAO (Vietnamese reading) / Blank. 23mm, 2.03 grams. Probably cast sometimes in the 17th century. Vietnamese Coins (2003) #485 var.
Small coin, probably a private issue
The Nguyen lords issued anonymous coins generation after generation. They are not well-studied and understood, but the larger copper pieces in 16th century style seem to belong to Nguyen Hoang himself and were issued during the earlier part of his reign.
Nguyễn Hoàng (15251613) was the first of the Nguyễn lords who ruled the southern provinces of Vietnam between 1558 and 1613, from a series of cities: Ai Tu (155870), Tra Bat (15701600), and Dinh Cat (modern-day Huế) (160013).