16x24x3-butt-plate; about .653" wide, .958" high and .128" thick. The hole in the center is about .156" in diameter. Butt plates are used at the pommel end of the handle, with or without an end nut. A particularly neat application is to file the end of the tang to a rectangle and file the hole to match. Or you can just file the tang to match the hole. Peen the end of the tang to anchor it.
We added these for the smaller handles so there was not as much grinding involved.