Spool Holder with screw mounts

I needed a filament spool holder for all the spools I'm now collecting, but all the ones I saw lacked a way to attach it to a shelf or table using screws. I didn't want the holder to slide around or vibrations to move it around, so screws are a must, and that is what this design does. What I like best about this holder is that I can use shelves that I already own and securely store the filament on that. If one day I want to use that shelf for something else, I can by simply removing the holders. I suggest using at least 1x8 shelves to fit the holder and spool. Medium size Command Strips will also fit in the area where the screws go if you want to use that instead. It has spots for 4 screws, but I only use 2 to save on costs and put them diagonal to each other.