Artificial stone and substitute for Ara-to. The stone of the groundwork, used before Binsui-do. Kongo-do is used when the sword is rusted or has a flaw. No. 80 is used especially when the sword is rusted heavily. It should not be used heavily as it takes away a lot of metal. Dimensions 20 x 5 x 5 cm, weight 1.6 kg.