I recently found myself with a bunch of empty Bambu Lab spools, and silly me, I tossed the cardboard inserts from the centers. I plan on using these spools as respool target spools, so I need something inside there to hook the filament on to. I loved the design concept used by Kaelen, with the straight-thru hole to hook your filament on, but I didn't like that there was only 1 hole. Also, when I printed his, I found the sides to not be as smoothly rounded as I'd like. So, I popped into Fusion and built this, taking inspiration from Kaelen's use of the hole, but I've made 4 such connection points, with them spread around the circumference.

Update (6/16/2025): I decided to rebuild this model with some slight enhancements. The core is slightly thicker now, resulting in better looking prints - less likely to have weird spots by the holes that grab the filament now. 

The pics here show the spool cores printed in 3D Fuel's PCTG Pro in Charcoal Gray. Turned out very nicely! If you plan on drying high-temp filaments, PLEASE consider printing in something better able to withstand the heat, such as ASA, PC, or PET (note, not PETG). If you're only ever going to use PLA or PETG, you don't need high-temp filaments.