This is a pencil holder from the late 1880s. My example came with some slate pencils and what might be an original Eagle pencil from that era. The Eagle “Ready Companion” is a wood tube with a spring-loaded button on the end that opens a ball at the other end. Ads and patent are dated 1887. The ad states that the pencil holder came with “a lead pencil, a slate pencil in wood and open holder.” It has an interesting design similarity to the Eagle Arrow retractable dip nib holder.
Video of the Ready Companion in action. Click on controls at bottom of video if not playing.