The spool holder that comes with the Cobbler's Sewing Machine is too small to hold a cone of thread. This adapter fits on top of the metal rod and holds the cones of thread I have. I printed mine with PLA at 40% infill and has been holding up fine. After printing, I did clean out the hole with a drill (but make sure to only drill far enough in as to keep the base of the holder off the frame of the machine). The Cone Bushing works with some of my spools, but is too large for others.