After setting up some IKEA Kvissle letter trays on my IKEA Kallax shelves, I ran into an issue with the walls on the Kvissle trays bowing outwards and releasing/dropping the shelves. These clips are designed to be attached to the interior walls of the Kallax shelves to prevent the walls of the Kvissle trays from bowing outwards, and keep the racks from sliding off the Kallax shelves at the same time.

They're designed to have one clip on each side of the Kvissle.

I printed mine out of PETG mostly as a test run for a PETG I hadn't used before, and so can't speak to their durability when printed out of PLA.

The step file has a 3mm countersunk (to 5mm) screw hole, to match the #4x1/2in wood screws I happened to have lying around in the garage.

The attached f3d file has a set of parameters ("screw_hole_diameter" and "screw_hole_chamfer") if you need to adjust it for a different size of screw. I'd avoid anything much longer than 1/2in or 8mm if you intend to mount more than one Kvissle side-by-side, as the interior Kallax shelf walls are only about 16mm thick.

The file also has parameters for the other dimensions, if you have any use for similar clips of different sizes.