I tested it with cord diameter 2-4mm. Flat cords can be ~6mm thick. 

There are different sizes available (2 at the moment).
They differ mainly in angle. 15° provides better locking but has less space for thicker cords.

Print as shown in the picture. Brim for the case is recommended. I used three walls and 30% infill for PETG.

Assemble parts as shown in the GIF. Make sure that knobs are pushed in the same amount to ensure easy sliding of the wheel.
Knobs can be glued in but it was not necessary for me so far.