Balboa / Gecko heater o-ring gasket seal to fit all Balboa M7 & non-M7 Heaters and many others including Gecko, AEware, Hydroquip, Aquatemp, RMF, and others. May be black, white, or clear material. Should be replaced every few years, or when there has been a chemical balance problem.
These have been White, Black, or Clear. All are interchangeable, but differ in price.
Two (2) are needed at each end of the heater.
Outside diameter: 74mm
Inside diameter: 53mm
Total Thickness: 6mm
Square edged O-ring side - diameter of raised ring centre to centre: 63mm
May Have Part Numbers: 711-4031, 21619, B-21619