Standards for Redemption of Soiled or Mutilated Currency Notes and Coins Unfit for Circulation Article 7
Coins may be redeemed at full face value if less than 5 percent of statutory weight has been lost through normal wear, and they are still identifiable by means of characters or patterns.
中文原文 污損破損不適流通之紙幣及硬幣收兌標準第7條
硬幣自然磨損，致法定重量減少未達百分之五，而其文字及花紋仍可辨認者，照全額收兌之。