China, 718-907 AD., Tang Dynasty, middle - late Kai Yuan type, 1 Cash, unlisted.

China, Tang Dynasty (618-907), Tang Dynasty, middle - late Kai Yuan type, issued ca. 718-907 AD.,
Æ 1 Cash (24 mm / 3,12 g), cast, square central hole,
Obv.: 開 元 通 寶 , Kai Yuan Tong Bao ("The Currency of the K'ai-yuan Period" or "The Inaugural Currency") , top-beneath-right-left of central hole; small crescent (or star?) at 5, star or dot at 11. The "jing" component of "Kai" touches the hole, the top stroke of "Yuan" is longer, left shoulder on "Yuan", the two stokes in the middle of "bao" do not touch the verticals.
Rev.: plain (square center hole).
cf. Hartill 14.4 and 14.13 ; cf. Schjöth 312 .
Stars are found less often on the obverse of coins than on the reverse. Hartill lists no coin with two additional stars on the obverse.

Kai Yuan meant “to open a new beginning”, and it did indeed set new standards for casting, legend, style and shape, that were followed in almost all later dynasties. The legend of Tang coins consisted of four characters read top-bottom-right-left.

J. Williams (ed.), Money: a history (London, The British Museum Press, 1997):
"The Chinese inscription on this coin reads 'Kai yuan tong bao', arranged top-bottom-right-left around the square hole. The characters 'Kai yuan' mean 'new beginning', while tong bao means 'circulating treasure' or 'coin'.
In AD 621 the first emperor of the Tang dynasty, Gaozu (reigned 618-626), established a new coinage system which had a profound influence throughout East Asia. The new Chinese coinage had a decimal base, with each coin weighing a tenth of a Chinese ounce and measuring a tenth of a Chinese foot in diameter. From this 'new beginning' the new coinage system lasted for over 1200 years.
The coin shown here is a standard Kaiyuan tongbao coin. A later development to the Kaiyuan came after AD 845 when over 4600 Buddhist monasteries were closed in China, releasing a large quantity of copper from statues and bells, which was entrusted to regional mints for recasting into coins. In the Huainan region of southern China, the character chang (an abbreviation for the Huichang reign period of AD 841-46) was cast on the reverse of coins. From then on, the government ordered each mint to put a single character on the reverse to indicate the place of issue. These coins are known as Huichang Kaiyuan coins."

開元通寶 Kai Yuan Tong Bao (The Inaugural Currency).
This was the main coin issued by the Tang. It was cast for most of the dynasty, a period of nearly 300 years. It was first issued by the Emperor Gao Zu in the autumn of the 4th year of the Wu De period (August 621). Its diameter was to be 8 fen. The weight was set at 2.4 zhu, ten to the liang. 1,000 coins weighed 6 jin 4 liang. The legend was written by the famous calligrapher Ouyang Xun in a much admired mixture of the Bafen and Li (official or clerkly) styles of writing. This is the first to include the phrase tong bao, used on many subsequent coins. The inscription was used by other regimes in later periods; such coins can be distinguished from Tang coins by their workmanship. Minting and copper extraction were centrally controlled, and private casting was punishable by death. For the first time we find regulations giving the prescribed coinage alloy – 83% copper, 15% lead, and 2% tin. Previously the percentages used seem to have been on an ad hoc basis. Actual analyses show rather less copper than this.
A crescent-shaped mark is often found on the reverse of Kai Yuans. The legend is that the Empress Wende inadvertently stuck one of her fingernails in a wax model of the coin when it was first presented to her, and the resulting mark was reverentially retained. Other imperial ladies have also been proposed as the source of these nail marks, especially the Imperial Consort Yang. Peng explores the possibility of a foreign source for them. More prosaically, they appear to be a control system operated by the mint workers.
At first, mints were set up in Luoyang in Henan, and also in Peking, Chengdu, Bingzhou (Taiyuan in Shanxi), and then Guilin in Guangxi. Minting rights were also granted to some princes and officials. By 660, deterioration of the coinage due to forgery had become a problem. The regulations were reaffirmed in 718, and forgeries suppressed. In 737, the first commissioner with overall responsibility for casting was appointed. In 739, ten mints were recorded, with a total of 89 furnaces casting some 327,000 strings of cash a year. 123 liang of metal were needed to produce a string of coins weighing 100 liang. In the late 740s, skilled artisans were employed for casting, rather than conscripted peasants. Despite these measures, the coinage continued to deteriorate. In 808, a ban on hoarding coins was proclaimed. This was repeated in 817. Regardless of the rank of a person, they could not hold more than 5,000 strings of cash. Cash balances exceeding this amount had to be expended within two months to purchase goods. This was an attempt to compensate for the lack of cash in circulation. By 834, mint output had fallen to 100,000 strings a year, mainly due to the shortage of copper. Forgeries using lead and tin alloys were produced.
In 845, in the Huichang period, the Emperor Wu Zong, a fervent follower of Taoism, destroyed the Buddhist monasteries and used the copper bells, gongs, incense burners and statues to cast coins in various localities. These local mints were under the control of the provincial governors. The New Tang History states that Li Shen, governor of Huainan province, requested that the empire might cast coins bearing the name of the prefecture in which they were cast, and this was agreed. These coins with mint names on the reverses, known as Huichang Kai Yuans, are of poor workmanship and size compared with the early Kai Yuans. However, when Xuanzong ascended to the throne the next year, this policy was reversed, and the new coins were recast to make Buddhist statues.
Archaeological discoveries have assisted numismatists in dating various varieties of the Kai Yuan more closely.