this is a model of a container and lid that fits into the center of nova filament spools. I've found that once you've used about half of the filament from a spool of nova filament in a creality cfs it doesn't weigh enough to always retract properly. by adding 5 steel balls .93" in dia. (10.2 oz) the spool engages the drive tires better and eliminates the retract error that you get when the filament doesn't retract all the way in the new creality k2 plus and cfs. the lid is held in place by feeding a piece of filament through the hole near the top of the container. be sure to leave this lock wire long or else you may not be able to open the container.