The idea for this came from Thing 11977, although the design is all new.
Basically, it's an apparently impossible dovetail joint that opens by rotating. My interesting little observation was that it needs almost no thickness, and no core, in order to lock and rotate well. It's a tiny empty box. As a result, this prints in a few minutes on our MakerGear M2 -- it prints better and nicer scaled-up 2X.
There are two versions here as STL files: one with the new University of Kentucky logo on one side and our department name (ECE) on the other, and a second plain version. The logo one was made in quantity and handed-out to EDay Open House visitors to our lab; interestingly, we had no problems fitting pieces together that were made on either of two MakerGear M2 and one Wanhao I3.
Printed in 0.25mm PLA scaled-up 2X. Prints as well on the Wanhao I3, but takes a lot longer than on our MakerGear M2.