Hi,

I've been using and testing a few spool holders in the past few month since I started 3d printing.

My favorite is this one here: 
Elegoo Neptune 2/3/4 spool holder with bearings by XMAN_Prints (picture 10)
https://www.thingiverse.com/thing:4971375

For my new prusa MK4 I printed then this one: 
Original Prusa Spool Holder Remix by DaHouzKat (picture 7)
https://www.printables.com/model/532057-prusa-spool-holder

But I'm not a fan of putting a spool directly on top of a printer, so after some search I found this beauty here: 
Spool Holder - 2kg, 1kg, 250g by Hugo (picture 6)
https://www.printables.com/model/724934-spool-holder-2kg-1kg-250g

Because I didn't want to throw away the other two spool holders I came up with the idea to design two adapters. My efforts were fruitful and now I can use all 3 together.

Tested and designed for:
Original Prusa Spool Holder Remix >> 77mm Version
Spool Holder - 2kg, 1kg, 250g >> 1Kg Version
If the other versions of the spool holder work with my adapters I can't say.

Printed on prusa MK4 with:
material: PETG, no-name brand
layer height: 0,22 mm
perimeters: 5 for adapter Original Prusa Spool Holder
perimeters: 7 for adapter Elegoo Neptune 2/3/4 spool holder
supports: yes
brim: outer brim only, 20 mm
infill: gyroid at 15%
nozzle: 0,4mm
print orientation: as in picures 4 & 5
print time: ~1h40 & 2h10 with the standard MK4 Input Shaper 0,4 profile for me

To use it you need to download the corresponding parts of the spool holder you want to use.

For the Original Prusa Spool Holder Remix you need to drill a hole on the bottom side of the holder and a M4 screw, washer and nut to prevent the holder from spinning.

Know issues:
The indentation for the M4 nut in the adapter for Original Prusa Spool Holder Remix  is a bit to wide (at least for my M4 nut).  It tends to rotate if I overtighten the screw. Some glue might help, or just do not tighten to much, it is only a stop against spinning.


Happy printing!