Simple double-cone tool that screws together from opposite sides of a filament spool to hold it for rewinding. Should fit most 1kg spools with 48-58 mm inner diameter and reasonable thickness, and most mini spools all the way down to 42 mm inner diameter. Each side has a 13 mm hex inset, intended to be driven by a M8 bolt in a drill chuck.

This can be used to respool:

• filament that was poorly wound
• filament that's wound onto spools that don't fit one's dryboxes, multi-material feed boxes, etc.
• filament that's wound onto printed spools incompatible with one's drying setup
• filament that fused into a brick from drying too hot (don't ask) after prewarming to soften
• filament that you want to move onto sub-1kg spools to share with friends, use on multiple printers at once, etc.

Printing doesn't need supports or any special options or materials. For the threads to print best you should probably use 0.2 mm or thinner layers and 0.5 mm or wider line width (even with 0.4 mm nozzle), but they do the job even if they don't come out perfect. 15% infill should suffice; even 10% is probably okay.