The file 'Ender3 V3 SE Spool Holder Frame, Balancing Weight To The Center 3D Printer Model' is (stl,scad) file type, size is 128.8KB.
The spool is rotated 90º, and moved so that the spool hangs above the gantry in the middle of it, making centre of the mass right at the center. It zeroes out all possible torques caused by filament weight, resulting into more consistent printing.
Source: https://github.com/avsd/filament-spool-holder-frame-for-ender3-v3-se
UPDATE: Added a variant with pins (not tested!), that should make it double-sure the holder would never detach accidentally (although it wouldn't detach even without the pins).
UPDATE 2: Added elevated version, for 2kg large diameter spools.
elevated-pins.stl | 107.3KB | |
elevated-spool-holder-with-pins.stl | 447.2KB | |
pins.stl | 106.7KB | |
spool-holder-with-pins.stl | 447.8KB | |
spool-holder.scad | 6.1KB | |
spool-holder.stl | 374.9KB |