I have the need to hang some of my active filament spools from vertical surfaces because I don't have much space at my printer. Because of this I designed a way to hang them with nearly no friction (see this). Works great unless the spool doesn't have an inner lip to hang by. I use a fair amount of Elegoo material and their spools are plastic and don't have said lip. This adapter snaps into those spools and allows me to use my hanger system. These will probably also fit other plastic spools but that's up to you to confirm. I used PETG, 0.2mm. FreeCAD file included so you can adjust as needed. Don't shoot your eye out.