 Under the reign of the Tang dynasty the number of Chinese cash coins with "flower holes" started to increase and circulated throughout the entire empire, concurrently the casting of Chinese cash coins was switched from using clay moulds to using bronze ones, however the earliest Kaiyuan Tongbao cash coins were still cast with clay moulds so the mould type alone cannot explain why these "flower holes" became increasingly common.As mother coins (母錢) were used to cast these coins which were always exact it indicates that these "flower holes" were added post-casting, the largest amount of known cash coins with "flower holes" have very prominent octagonal holes in the middle on both sides of the coin, comparatively their legends are usually as defined as they appear on "normal cash coins", for this reason the hypothesis that they were accidentally added is disproven.All sides of these coins (either octagonal with "flower holes" or hexagonal with "turtle shell holes") are clearly contained inside of the cash coin's central rim.