I modelled the idea I had during the conclusion stage of the previous log. It's a proof of concept, so the actual 3D file is somewhat fragile at the moment. There's little benefit for perfecting things now when the idea might not even get green-lit by fabs or geometric conflicts arise when designing the heatvalves and heatsinks.

I looked into the old-school all-metal heatbreaks and they use 3.2mm at the tube section. I believe I've also seen more recent hotend designs (like the SV08 in the previous log) use 3mm tube. 

Currently, I've modelled 1.8mm ID 2.8mm OD tubes to try and balance powder removal, ease of drilling and lack of heat conduction.

The issue I see at the moment is the sealing of the heatblock to the heatvalve. Perhaps they would have to be integrated too?