http://www.thingiverse.com/thing:52946 . The video shows two parts, an S-Shape hole and an S-Shape plug http://www.thingiverse.com/download:1... . The plug and the hole are edge to edge touching each other in the STL file. As show in the video, I can actually plug them together just by pushing real hard with bare hands, no tolerance compensations in the design, no drilling or filing, they just fit. The S-Shape is chosen deliberately as it shares a lot of common features with interlocking designs. Designing is fun with interlocking designs.