Artificial stone and substitute for Ara-to. The first stone of the groundwork, used before Binsui-do. Kongo-do is used when the sword is rusted or has a flaw. No. 120 is used when the sword is rusted heavily. It should not be used too heavily as it takes off a lot of metal. Dimensions 20 x 5 x 5 cm, weight 960 g.