The part number that Linguster gave is correct. They do come 8 in a bag. They are optional o rings for serpent cars but not exclusive to the eryx, I'm sure they fit all the on road cars shocks. I found they worked well for me and were not too loose or too tight. They provided a good seal on my shocks. In fact it was better than all the other seals that I had from previous cars that I tried. I did buy the delrin bottom inserts that you put into the bottom aluminum shock caps.
After the enduro that I ran, 3 of the 4 shocks were still nice and did not leak or suck in air. One shock did, but I noticed that one needed some work before the enduro even started to be perfect but I ran out of time to fix it. We finished 2nd with no breakages or issues except the motor was extremely slow for some reason.
Steve