All you need are 9mm dowels to make these work.

They will hold the spools in a way to easily see the colours and make it easy to grab one from the middle. 

One set is taller than the other to allow you to easily have two rows of filament and see/access either row

the dowel stop is simply in case you get a 7/8 mm dowel that isn't pressure fitted. In that case, you can still use these mounts, but might want the dowel stop and some small screws to keep the dowel properly aligned.