When i encounter these i have a long pair of needle nose pliers that can open wide enough to sit in the middle grooves/notches of the ring, then i keep pressure on them as i try to turn the ring, or place channel locks on the needle nose pliers as i hold the pliers in the grooves and use the channel locks for leverage to turn the pliers as i hold the pliers in the grooves, the pliers apply equal pressure to the ring when turning vs the trying to tap the ring loose by hitting only one side of it.
Are you experiencing some weak jets compared to the other jets as your reason for replacing these?
Or are some of them missing and you just want to have them all match up again by replacing the missing ones?
Why are you replacing them?
Are all of the jets equal in how they operate, or do 1 or 2 jets only have water returning, while the others have both air and water?
I can tell you as old as yours appear to be in pic, that they can easily break, as you have experienced already when trying to remove them.
I intentionally have removed, or broken them out before, and not replaced them, because the jets work better without them, in many cases.
Really though, why are you replacing them, my thoughts are because there is uneven jet action and you think this may be the problem, when it may not be, so first explain why.
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