I'm afraid I'm in the same boat as rrhb - I don't know what the insets are. I like the extruder design, but there is a hexagonal hollow inside of the body that appears to serve no purpose (other than to create a space for the filament to get kinked in). Does this somehow get filled in by the inset?? Are the insets meant to be printed separately and then inserted into the body, or are the somehow merged as meshes and sliced together? I also don't understand the difference between the 16.4 and the 16.7 insets and why the 16.7 would need a better-tuned printer. I feel somewhat dumb for asking these questions, but there really are no instructions given here.