When the @humebeam silica gel spools get a bit old [and take on moisture], the thread becomes very tight and they are impossible to unscrew with bare hand power. This tool is textured with 2mm bumps to help grip and unscrew the threads.
I printed mine in PLA with three walls, and 20% gyroid infill to handle the torque.
The author remixed this model.
Here's a spool tool that matches the shape of the silica gel holder spool.