Formerly, there was a rule according to which geshaku was used by persons of the Goi (Fifth Rank) or above, and mokushaku was used by persons of the Rokui (Sixth Rank) or below; later, however, geshaku came to be used during formal attire (court) and mokushaku in other occasions, regardless of the rank of the holder.
かつては五位以上の者は牙笏、六位以下は木笏と決まっていたが、後に位階に関係なく礼服(宮中)のときにのみ牙笏を用い、普段は木笏を用いるようになった。