Model originally uploaded to Thingiverse at https://www.thingiverse.com/thing:2054533.
This is a top mounting filament spool support for Kossel Delta printers with 2020 (20mm) extrusions and 240mm extrusion side lengths (to suit Ancubic Kossel Linear and similar models). It's designed to fit a Hard Drive Bearing/Motor (which came from an old 3.5" Seagate Barracuda 80GB drive). It prints as three identical parts, which attach to the side rails with two M4x10 screws and M4 nuts. It includes a 3mm hole to mount the bearing. Obviously this may not fit all bearings, and some modifications may be needed to suit different types. There's also a connector model included, which is used to connect the arms together with M4 screws. The whole assembly is designed to be very low profile, so the spool is almost touching the top rails.
Note: this is designed as an "exact fit" making the tolerances very tight, so this is very unlikely to fit straight off the printer and will need some filing and trimming. I measured after printing and it was slightly over size, so I filed the front and rear faces of all the arms until they just fitted. I also cut the "teeth" off one of the parts, so it could be slid in from above without removing the side rail (although it would be possible to remove the side rail temporarily to fit).
The Sketchup model is also included for ease of editing, and this also includes a 3D model of the Seagate hard drive bearing for comparison.
To mount the filament spool to the bearing, I made these two adapters: http://www.thingiverse.com/thing:2052951 http://www.thingiverse.com/thing:2340642
Note that the photos don't show the final routing of the filament: I plan to move the extruder and add filament guides.
If you have a different HDD bearing, you might need an adaptor. Here's one made by cwalker74 for a 1TB Seagate HDD: https://www.thingiverse.com/thing:2598023
I've recently uploaded an (untested) variant for the Linear Plus (spool_arm_linear_plus_01.stl) which should suit printers with 300mm extrusion length instead of 240mm.