Now that I have my printer working enough where I want to do some prints and I have a 1kg roll of filament on the spool bolt I've found that it just doesn't hold too well.
Why not add some "horns" to your printer! These should be easy to print. You'll need to use supports. I printed with the notched side down to the bed. This may require you to have support for the catch portion of the holder. You can always print it with that side down as well. Either way you'll need supports.
These have a notch on the side that goes up to the metal spool holder bracket.
Take the bolt, nuts, and washer off the metal holder. Put the bolt through the washer and then insert the bolt down the length of the printed spool holder and through the metal bracket. The notch in the end of the holder should line up nicely with the bracket. Then use one nut to secure the new spool holder.
There are two STL files, one for E0, the left primary extruder, and another for E1 the secondary extruder. They're the same really, just mirrored. I made two STLs for those who don't know how to do the mirror function in their slicer.