If you built the Prusa Lack enclosure, you will recognize this item used to connect the enclosure to the base and also to support the Plexiglass and door hinges. If you want to add a third table, you need something similar or the top two tables would fall off--except the hinges and supports aren't needed. So these are matching corners without the door hinges and Plexiglass supports.
The cup is screwed to the bottom of each leg, and the other piece is screwed to the top of the table in the four corners.
These are identical to the Prusa original items, although they are not a remix because I modeled them in Fusion 360 from scratch. My compliments to Josef Průša, his awesome company, and the original designer of these parts.
Each unit is attached with a 3/4" #14 wood screw, or the equivalent metric equivalent.
The author hasn't provided the model origin yet.