I tried the nut calumet designed by MoonCactus ( http://www.thingiverse.com/thing:44118 ) but the nut holes were too tight so I designed the same tool to myself. There're two sticks - one with 6.4mm and another with 6.8 mm nut diameter. The smaller holds the M3 nuts tight meanwhile the wider fits easier on the nut.There're two holes for the M3 nuts - one on both sides.I printed from PLA. My print settings: 20% infill, 0.1 mm layer height (I guess 0.2 mm works fine too), 210 C, standard 50 mm/s print speed, no support at all. Sliced & printed with Cura 12.12.