These are little hexagon thingies that fit the profile of the hexagon patterns on Prusa spools. You can stack and lock multiple spools togeather this way. If ever want to do a project with empty Prusa spools, these could come in handy. 

Note that the hexagon patterns should be in the same orientation to work. Align the labels on the spools to make this easier. 

Here's the Onshape file in case you want to make edits to it yourself
https://cad.onshape.com/documents/8a234c3aa2ebb9771f4506f5/w/d29bf426593d39d0e2e9ee9d/e/93a6fee8d02785b9126d14f1