This is a quick hack because none of the existing spool holders quite did what I wanted. This one clips onto the top triangle's 15mm extrusion and can be screwed in place without having to disassemble anything. The fit is pretty tight anyway, so the screw may not be needed.

Print instructions

Category: 3D Printer Accessories Print Settings

Printer: Kossel Mini

Rafts: No

Supports: No

Infill: 25%

Notes:

Prints fine on its side.