This part is for the very specific case where you accidentally break the tiny flimsy metal arm off of an IBM Selectric's paper table. It slides right over the end and friction fits into place.

The part is specifically for the left side, but if you want one for the right side you can just mirror it in your favorite slicer. It's also specifically for a Selectric II but it looks like the paper table for the Selectric I might be the same design.