I wanted to have an "impossible passthrough" style model that

• is small so I can print one for everyone in a group, as a surprise present
• is sturdy
• works well
• has maximum possible detail for the size
• both parts should seem like a full size part (maximizing the illusion)

This is as good as I got.

There are two inserts, one in cube form and one cylinder-shaped. The cylinder is easier to use if the print is not perfect. The cube gives a nicer look.

There is a version of the outer part with “adhesion ears” that can be broken off. (There are small holes in the flange to control extrusion direction during slicing. Without the holes, there is increased danger of ripping parts out of the main body when breaking off the ears.)

The model already has good tolerances, so no XY-compensation should be necessary on either part.

I included the Fusion360 file for remixes.