Mrk3 of my modified Sermoon V1 fan duct.

Please read the original setup info from here : https://www.thingiverse.com/thing:5868023

There are 3 main improvements. :

1) The air flow is much better than before. The air is more directed towards the center of the nozzle and just below it. To achieve this, the geometry has been changed to flare out then funnel air towards the nozzle. Also, reduced back pressure, due to the constraints of the fans placement.
2) Moved the duct fins out away from the hotend by a couple of mm, so it won't melt as easily.
3) Now in parts so you and change to a Volcano nozzle by using the spacers. I use klipper which allows the print height to be changed easily. Allowing this mod. If you have a Cr-Touch, then you will also need to make/use a spacer for that chosen mount. Use the Volcano nozzle/variant at your own risk.

For a standard nozzle this duct requires 3 M3 nuts and bolts, minimum of 7mm in length. A longer size is needed when using the Volcano nozzle spacers, 18mm or a little more will work.

I would recommend that the user bolts the connectors to the correct side of the fan duct, as seen in the render, before attaching the complete duct to the printer.

Recommend to print the original duct which this is a remix of, so you can print the long bridges which this one contains.

I use OrcaSlicer 1.8.1. which is a great slicer.
0.2mm layer height
0.4mm line width

Use PETG filament or, if possible, use CF-PETG as I have found that it is very resilient against the hotend heat.

Also, I now use this improved CFM fan by GDSTIME :
5015 Blower Fan 24V Brushless Dual Ball Bearing Turbo Cooling 50x15mm 2Pin 39 inch Cable for 3D Printer Hotend Extruder