I kept having to take down and replace the spool of filament on the standard spool holder that came with the printer and had no place to put the second one. So now I can leave one hanging while I print with one, and then quickly change to the other filament either on the next print or during the print.
This fits directly on the metal bracket that came with my CR10s Pro Printer.
I included two female couplers, one is a tight fit, and the other is loose. This will depend on your use of supports when printing. If you do not use supports everywhere, then I would suggest the loose fit coupler.