Name this tool

[Ron Nossaman]

>Ran across one of these today. The back-side is labeled "Steinway &
>Sons". The tool is on top of a CD case in the photo for
>scale/perspective. The slot leading off to the left os about 1/4" deep,
>whereas the mortice to the right of the slot is more like 3/8" deep.
>There is a square of buckskin visible in the photo at the right end of
>the mortice. Anybody know what this is?
>
>Mark


I think the technical term is backcheck driver-inner.

Ron N