Important notes: 

• Print out of ABS, ASA, or PC-ABS with Voron print settings.  (40% cross-hatch or gyroid infill, 5 walls, 5 top and bottom layers,  forced .4mm line width on all line types). 
• This will work for both the Neptune 4 Pro and the Neptune 4 Max.  It should also work for the Neptune 4 Plus but I have not been able to test that. 
• If you don't feel that I spelled anything out well enough for you, I am sorry.  I didn't want to become the only person to have pulled this off and I didn't really keep notes of how I did it.  Please try to get there yourself and only ask me questions if you get really stuck.

This one took me weeks and more than a dozen iterations to get right.  It allows you to mount a Stealthburner to your N4Pro securely. 
 

BOM

M3x4x5 Heat Set Inserts - 10x - https://amzn.to/3VT0evT 

M3x8 SHCS - 1x - https://amzn.to/3VTpemI 

M3x16 SHCS - 3x - https://amzn.to/3L1YRop 

Everything else should be part of your Stealthburner setup.  

Modifications to existing hardware

It may be tempting to use the pancake motor out of your Neptune toolhead.  Don't.  That was a week of pain.  Buy the one that the stealthburner recommends. 

The bed sensor from the old toolhead can be re-used.   It requires that you set the NPN jumper and the sensor voltage jumper to 24v.   You will need to extend the wire for it.

How to make the printer work:

I will likely not be releasing a step-by-step guide for how to get this to work in the software as that process has taken me months.  But the broad strokes are: 

• OpenNept4une - Required - https://github.com/OpenNeptune3D/OpenNept4une 
• BTT U2C v2.1 - https://amzn.to/4bud7S1 
• BTT EBB SB2209 - https://amzn.to/3VQbysU 

When you make the Stealthburner, I highly recommend that you get the modified files in the ERCFv2 project that have the Filament Cutter and the dual filament sensors in the toolhead. https://github.com/Enraged-Rabbit-Community/ERCF_v2/tree/master/Recommended_Options/ERF_Filament_Cutter/Stls 

Update V2: Raised bed sensor by 2mm to fix collision issue.