This is a adapter for mounting two lack tables together. You need one for each table leg. Don't have to use extra screws but it's possible as there is a hole provided. it's screwed to bottom table by it's leg's screw. Very stable until you kick the table :) model provided sets upper table 100mm higher. I recommend my solution for mounting two tables together. There is only some mounting for plexi glass missing for future extension.

This thing was created in FreeCAD which has it's portable versions I recommend, for Windows download "portable" one, for Linux an "AppImage" from here: https://github.com/FreeCAD/FreeCAD/releases. Then you can customize the thing to your needs.