Replacement electrode for the  R-20 / R-40 / R-50 and AE-50 models, the R-200 model from 25 years ago and many competitors.  Unique one-piece capsule screws into any 2” threaded tee and keeps electrodes out of the direct flow of the water for longer wear and tear.  Clear viewing window for cleaning and replacing purposes.  Requires Teflon tape when screwing into tee.  3” long electrodes, 1 ¾” “half-moon” in diameter.  Schedule 40 PVC.   Price includes free shipping in the USA.