This model is designed to fit the Overture cardboard spools in an effort to add weight to them as they run low on filament so that they are more compatable with the AMS. They also fit the Bambu spools as they have the same inside diameter hole. It is a 2 piece design, which screws together to hold the weighted material of your choice, and keep it retained in the center of the spool. For weight, I used copper plated steel .177" BBs, filling about 90" of the base piece, and then poured 2-part casting epoxy resin to fill in the gaps and to provide a solid piece so that the BBs don't fall out when changing to a new spool.