A series system consists of a retaining ring, a non-threaded filter, and the adapter. Different types of Series filters can be used with just one pair of adapter and retaining ring, or you can have various adapters for different lenses, and still just use the one set of filters.
Of course, the diopters and the lens hood are also used with the adapter, and the lens hood simply screws onto the adapter without using the retaining ring.
Now that I have assembled a kit to go with my CCTV lens, I realized that I have many extras in the boxes of accessories in my basement. After some sorting, I have enough parts to put together 4 sets of Series VI adapters + a set of diopters (+1, +2, +3), and a yellow filter.
No diopter, here, just the lens hood. That 25mm lens is just awesome!