This filament spool holder fits onto the Ultimaker2 and holds filament spools with a small diameter hole.More pictures and details here: http://www.eleccelerator.com/3dprint-drillbit-box-ultimaker-filament-spool-holder/ STEP and SolidWorks files are availableUPDATE: recommend instead https://youmagine.com/designs/f26-um2-bearing-spool-and-bearing-guide-upgrade