These are little clips that help keep the lid from falling of the smaller SAMLA boxes from IKEA. This clips works with the 5L, the 11L and the 22L boxes and their lids.
The clips have a little wedge sticking out that holds the clips firmly in place when the boxes are stacked on top of each other.
When 2x 5L boxes are stacked side by side on top of the 11L or the 22L box, you need to place the clips so that they are slightly off, so that they don't hit each other in between the boxes.
You can leave the clips on the lid in one side, and simply open up and detach the lid.
IKEA sells similar clips for the bigger SAMLA boxes, but they don't work with the smaller ones.
I usually print a plate of 4 on the Ultimaker, but do it one by one, so that if something goes wrong during the print, I won't have 4 failed pieces, only one.
It also prints them nicer, since the printing head won't need to move outside of the object.
If you want a wider clip, you can use customizer to change it, just put in how many mm you want as the width.