Model originally uploaded to Thingiverse at https://www.thingiverse.com/thing:1515475.
This is an upgrade for the stock spool holder design to add a guided offset for the spool of the back of the BigBox case.
The stock design works good for normal spools although I had an issue with black spools leaving black scratches in my polar white case which looks not very nice. The design definitely failed for me with 2.2kg productions spools from Colorfabb because the spool has a much bigger diameter so the spool can get in contact with the protruding screw heads.
To mount the spacers you need M3x30 screws instead of the M3x20, for one spool holder you need two spacers and 6 screws.
The second part, spool holder clamp, is not mandatory but recommended because of the increased distance the stock clamps are a bit short. To build these you need a M4x40 screw instead of the stock M4x30. One for one clamp.