The four racks in this model go together to make a symmetric sliding mechanism. It is a difficult puzzle to put them together, and even more difficult to have them slide together so that they all have the same offset relative to each other. Four endcaps fit onto the ends of the racks with a friction fit. Note that the various parts come wired together - the wire can be cut off with scissors.
For more details, see the video for the previous version at https://youtu.be/sDJk-9QxFro