Slip fasteners. The wooden or bamboo pieces used on the reverse side of the overlapped boards of a board-and-batten ceiling *saobuchi tenjō 竿縁天井, to prevent the boards from slipping, separating, or warping. The slip fasteners are attached to the overlapped boards by means of a shallow curved cut, hanejakuri 羽決, that is made on the edge of one board with the fastener rabbeted to fit across from the curved cut over the straight edge of the adjacent board.
There are two other common types of inago:
1 hon inago 本稲子, which has a rectangular cut with slanted sides, positioned precisely on the reverse side of a board in order to receive the slip fastener which slides in from the adjacent board.
2 tsuke inago 付稲子, which has a rectangular block with a tunnel cut secured to the reverse side of a board. A wedge-shaped slip fastener is then inserted from the adjacent board.