Aluminatus TrinityOne spool holder (two types)
by jeffwillden, published
There are other spool holders, but I like this design because the spool sits on top of the gantry and rotates freely. It slides in from the side, and the spool slides over the cylinder and rests, inclined slightly forward and feeds the filament down to the head.
There are two styles. One has Aluminatus branding and is larger, but holds the spool at more of an angle, where the other is small and hardly visible when in use, but still effective.
I printed the larger one with 0.1 honeycomb fill to use less filament, and the top layer did show some artifacts where it didn't close completely, but that surface is hidden inside the spool, so it doesn't matter.