Vietnamese Coin
Thien Thanh Nguyen Bao

Vladimir Belyaev
May 16, 1998
Obverse: Vietnamese Thien Thanh Nguyen Bao

Tian Sheng Yuan Bao

Reverse: plain

Diameter: 21.6 mm
Weight: 1.5 g

Obverse: Vietnamese Thien Thanh Nguyen Bao

Reverse: plain

Diameter: 22.1 mm
Weight: 1.6 g

Vietnamese origin of this coin is undoubt because of size, weight, reverse without rims, character style. But there is no unit opinion about period when this coin was issued.
Some authors mentioned that it's ancient Vietnamese imitation of Chinese Nothern Sung dynasty coin with legend T'ien Sheng T'ung Pao.

Obverse: Chinese T'ien Sheng Yuan Pao in seal style

Reverse: plain

Diameter: 25.2 mm
Weight: 4.4 g

Obverse: Chinese T'ien Sheng Yuan Pao

Reverse: plain

Diameter: 25.3 mm
Weight: 3.5 g

Nothern Sung Dynasty
The Emperor Jen Tsung 1022 AD - 1063 AD
Period T'ien Sheng 1023 AD - 1032 AD (Celestial Holiness)

Obverse: Chinese T'ien Sheng Yuan Pao in orthodox style

Reverse: plain

Diameter: 23.4 mm
Weight: 2.9 g

T.D.Luc:
It is Japanese Thien Thanh cast in Nagasaki to sell in Annam in 17th century due to the character NGUYEN.

Chinese Coinage Web Site