This is a very simple reverse Bowden connector for Prusa Mk2.5 or Mk3. Unlike the threaded connectors, it's very easy to take off, but it still holds firmly enough that retracting filament does not push it off.
The connector fits the filament cover of the standard MK3 extruder.
Force the PTFE tube into the connector from the top, the friction should hold it enough so it does not come out. When sliding the connector onto the extruder, make sure the notch is aligned with the bolt holding the filament cover.
Increase the number of shells so there is no infill (not worth it for such small part).