This is a small spacer that allows you to adapt the Xbox One controller thumbsticks to older xbox controllers including the xbox 360 controller, the OG xbox S controller and even the Duke controller without restricting functionality (full stick range and clicking).
These are meant to be fairly tight to snap onto the stick stem. If they don't fit you may be able to trim the inner parts of the spacer with a blade.
I tested on 5 controllers (two S, one duke, and two 360 controllers) and printed them out of black PLA.
The InterAct Powerpad Pro controller for the original Xbox is confirmed not compatible with this mod due to having a different style thumbstick module and are glued in.
The author hasn't provided the model origin yet.