I took the best elements of the Mk III and Mk IV designs, combined them, and scaled the design down to create the 1.75mm prototype nozzle seen here. The nozzle itself is machined out of a piece of 13mm x 13mm brass bar stock and is very similar to it's larger sibling. I machined the nozzle holder out of black PEEK and milled out the grooves in similar fashion to the grooves on the Mk IV. However, I also drilled out the center and installed an aluminum heat-sink tube to provide support and heat dissipation for the PTFE core. A small PEEK spacer is used to insulate the aluminum tube from the brass nozzle.
This hot-end ships out tomorrow for testing. If it is successful, I am planning to use the same concept for the Mk V as this design will allow for a shorter hot-end.