A nail used to secure the molds used in metal casting. When a metal statue was cast using the lost-wax method, a model of the desired form was covered in wax, and then an outer mold was constructed over this. The wax layer was melted away, and molten metal poured into the space it occupied, between the inner and outer molds. The kōgai was a nail which penetrated both molds and held them in position during firing and casting. Several kōgai were usually used, at the front, back, and sides of a statue. They ensured even walls and prevented warping. No examples of statues made using kōgai have been found from the Asuka period, but they were used in the Hakuhō period for casting the head of the Buddha in Kōfukuji 興福寺, Nara. In the Yakushi Sanzonzō 薬師三尊像 in Yakushiji 薬師寺, Nara, kōgai were used in conjunction with pieces of metal *katamochi 型持 inserted between the molds, serving the same purpose.