This is a spool holder designed for the 3D Printing Nerd Design Contest and was designed in Fusion 360.
It is designed to hold two 1kg spools from a manufacturer like Matterhackers, or three 500g spools from a manufacturer like Proto-pasta, while also minimizing torque on the two 3/4in mounting bars. It requires no mounting hardware, simply place it on the two beams and put your spools on! It has a 30mm threaded section to allow spools of smaller internal diameters to fit on it and also supports spools with a larger internal diameter. You can use multiple nuts to space spools apart or keep spools of different sizes in a certain spot. Additionally, the holder without the nuts weighs 100g, so you can even print 10 with a 1kg spool if you reduce the infill slightly! Each nut weighs approximately 12g, and the holder only needs one to function, but you can print as many as you like. To adjust the fit of the nuts on the threaded section, use the horizontal size compensation feature available in almost all modern slicers when printing the nuts for tighter or looser fits.