Filaflex has 2 types of spoolsizes. With these spoolholders they can be placed on top of the printer. Work in progress, so its design might be changed in the future.
In the Version 2 of the stl i changed the opening which goes on the printer and narrowed it to 5mm.
As the bigger spool weights it might be advisable to use a 100% fill to make the spool holder more stiff.