I printed a spool holder for my 3kg spool. This is the spool holder I used: https://www.thingiverse.com/thing:6154720

Then the spool holder snapped after I put on the spool. Therefore I created this support structure for the end of the spool holder to reduce the torque on the holder.

Edit: also you can support the spool holder on K1C(Tested) directly.