Three part spool. I wanted a spool, with full sides and bottom, I could use for winding a pound plus of filament on using my filastruder and filawinder and then mount on our Robo 3Ds. It's printed in 3 parts then glued together. I tried an armed type filament holder and sometimes the filament would get caught. Use either part 3 or use part 3 solid printed with 2 or 3 vertical shells. So far I have printed 10 and I've printed them both ways but I don't remember why!