O-ring for Adapter used on Fleck 5810, 5812, 7000 and other Pentair Water Products.Also on the 5810, 5812 and 7000 injector cap. Used on adapters that connect to Fleck 5810, 5812, or the 7000 By Pass or Valve to the water pipes. Also, used on a Quick Connect fitting for Structural CT ( contact tanks ) made after May 2008.