An Eraser of a Different Sort

This eraser attachment was made by Eberhard Faber and has a patent date from the late 1800s.

The eraser is a little bit thicker than the slot it goes into, so it sits firmly inside.

The assembly fits round or hex pencils, such as an Eberhard Faber Van Dyke…

…or a Castell 9000.

I wonder if this design was a stepping-stone to the clamp eraser.