When the Treaty of Amity and Commerce between the United States and Japan was concluded in 1858, the fact that about 8.6-gram ichibu-gin was coincidentally equivalent to around one fourth ryo in weight, which was worth of one fourth ryo of silver at face value, provided Townsend Harris with the excuse of insisting unfavorable exchange rate for Japan that three ichibu-gin coins changed one-dollar silver coin which was about three fourth weight of Chinese one ryo of silver and led koban flow out.
このため、安政5年（1858年）の日米修好通商条約締結の際、約8.6グラムの質量を持つ一分銀は偶然にも質量としての一両の約1/4であることから額面通り銀1/4両であり、中国の銀一両の約3/4の質量である1ドル銀貨＝一分銀3枚という日本側に不利な交換比率を主張する口実をタウンゼント・ハリスに与えることになり、小判流出の一因となった。