I put 2 of my IKEA PS cabinets on top of each other. To do this, I sawed off the legs of the top cabinet. Because I had done another project with the cabinet some time ago, I had of course wasted the end caps and needed new ones quickly. So I just designed a few replacement caps. Maybe someone else can use them, they fit all square tubes with an inner diameter of 17.5 mm and an outer diameter of 20 mm.