Ryukyuan mon in the context of "Vietnamese cash"

A string of cash coins (Traditional Chinese: 貫, 索, 緡, 繦, 鏹, 吊, 串, 弔, 錢貫, 貫錢, 貫文, 吊文, or 串文; French: Ligature de sapèques) refers to a historical Chinese, Japanese, Korean, Ryukyuan, and Vietnamese currency unit that was used as a superunit of the Chinese cash, Japanese mon, Korean mun, Ryukyuan mon, and Vietnamese văn currencies. The square hole in the middle of cash coins served to allow for them to be strung together in strings. The term would later also be used on banknotes and served there as a superunit of wén (文).

Prior to the Song dynasty strings of cash coins were called guàn (貫), suǒ (索), or mín (緡), while during the Ming and Qing dynasties they were called chuàn (串) or diào (吊). In Japan and Vietnam the term 貫 would continue to be used until the abolition of cash coins in those respective countries.

The cash or qian was a type of coin of China and the Sinosphere, used from the 4th century BC until the 20th century, characterised by their round outer shape and a square center hole (Chinese: 方穿; pinyin: fāng chuān; Jyutping: fong1 cyun1; Pe̍h-ōe-jī: hong-chhoan). Originally cast during the Warring States period, these coins continued to be used for the entirety of Imperial China. The last Chinese cash coins were cast in 1912, the first year of the Republic of China. Generally most cash coins were made from copper or bronze alloys, with iron, lead, and zinc coins occasionally used less often throughout Chinese history. Rare silver and gold cash coins were also produced. During most of their production, cash coins were cast, but during the late Qing dynasty, machine-struck cash coins began to be made. As the cash coins produced over Chinese history were similar, thousand year old cash coins produced during the Northern Song dynasty continued to circulate as valid currency well into the early twentieth century.

In the modern era, these coins are considered to be Chinese "good luck coins"; they are hung on strings and round the necks of children, or over the beds of sick people. They hold a place in various traditional Chinese techniques, such as Yijing divination, as well as traditional Chinese medicine, and feng shui. Currencies based on the Chinese cash coins include the Japanese mon, Korean mun, Ryukyuan mon, and Vietnamese văn.

The mun (Korean: 문; Hanja: 文, Late Middle Chinese: 文, romanized: mjun, Middle Korean: 문, romanized: mwun) was introduced as the main currency of Korea in 1625 and stayed in use until 1892. Prior to the mun, cash coins with the inscriptions tongbo (通寶) and jungbo (重寶) and silver vases called ŭnbyŏng were used as currency in the Goryeo Dynasty (918–1392), as well as imported Chinese currency. The mun resembled and was derived from the Chinese wén (cognate also to the Japanese mon, Ryukyuan mon, and the Vietnamese văn). Coins denominated in mun were cast in copper-alloys such as brass or bronze and were round with square holes. From the 17th century until the end of the 19th century, coins denominated in mun bearing the inscription Sangpyeong Tongbo (상평통보, 常平通寶), introduced in 1633, were the most widely circulated currency. In 1888, coins were struck in small numbers denominated in mun and won (written as "warn", which were equal to 1000 mun). The mun was replaced in 1892 when the yang was introduced.

The cast coins of the mun would remain in circulation long after their abolition. They continued to be legal tender in Korea at a value of 0.1 chon (1⁄1000 won) until 1908, when they were revalued to 0.2 chon, or 1⁄500 won.