I wanted to convert my E3D Titan Aero from 3mm to 1.75mm filament.
I knew you needed a new filament guide, and heat break, but also found out you need to replace the heatsink lid becaues the heat breaks are not the same. I ordered a fliament holder and when I got it, it was the left hand version where I need a right hand version for the Standard Titan Aero. The LH version is for the Mirrored model.
So I ordered another RH filament guide and decided to attempt to make my own 1.75mm filament guide. I measured the best I could and this thing is the result. It is working great to the point that even though I thought I would change it out when the new one arrived, I have now decided that I works well enough to leave alone.
I used PETg at .1mm layers with a 5 ring attached brim to help it stick better. ABS would also work. PLA is not a good choice for this purpose.
Some careful cleanup may be required to clear strings from holes.
I included all four possible versions, RH, LH, for 1.75 and 3.0 models here.