A few days ago i designed my
"Benchy Filament Sample Carousel & Sign-Generator"
( https://www.thingiverse.com/thing:3037172 )

In order to build a stable spool-tree, i need something that...

• holds them in place...
• while every spool still can be rotated easily
• add more spools later
• can hold different spools with variable inner diameter
• but the space between them is minimal
• 3d printing optimized (most parts printable, material reduction)
• threded rod used (also variable diameters)

so i came up with the idea of...

• a strong base, where a nut is glued in and that can hold M6-M12 threaded rods
• spools with inner diameters between 30-70mm are compatible
• the washers are independent from the threaded rods diameter...
• so the <>-shaped connectors were born

if you are not using the metric values for screws,
then try printing one of the TEST-files i uploaded and use the one that fits best.
alternatively you compare the values here:
https://en.wikipedia.org/wiki/ISO_metric_screw_thread#Spanner_(Wrench)_sizes

sadly i'm still stuck on tinkercad with my designing skills.
so i'm not able to create a customizable file for the washers.
but i added a bunch of them growing by 2mm each (30mm, 32mm, ..., 68mm 70mm).

Parts needed:

• (*) 1x threaded rod - 0.5m-1m recommended (size: M6-M12)
• (*) 2x nuts - or 1x nut and 1x butterfly nut
• 1x base (model depends on the size of your rod - no phun intended)
• 1x connector (same size as base)
• (**) 1x connector
• (**) 2x washer (model depends on the inner diameter of the spool)

(*) = not printed
(**) = per additional spool