This "thing" is all about presenting those CHEP cubes. You know what a CHEP cube is if you follow Chuck Hellebuyck on his Filament Friday YouTube channel (FilamentFriday.com). Chuck also has a very helpful website "CHEP Club" (www.chepclub.com). Both his CURA profiles and helpful videos on YouTube helped me be nothing but successful right from the start with my Ender 3 Pro. This stand will also hold any 20mm calibration cube.
The stand can be expanded horizontally and/or vertically using the "mending plates" and M3 screws (I used M3 hex socket button head cap screws). Typically I used M3x12mm or M3x14mm for the screws that go into the base plates and no longer than M3x8mm screws that go into the top of the backs to connect the next level above. There are also small clips that can be used to keep the base plates straight and not separate at the front. The clips come in large and small sizes although printing in PLA the small size typically works best. The large is provided for a slightly tighter fit.
Thank you Chuck for making this hobby so fun and removing all the stress out of getting started and being successful!