Waterway industry standard 2 inch o-ring gaskets part# 711-4030, designed to work with 2 inch flo-thru heater housings, with split nut unions and 1 piece plastic unions. You are getting a pair of gaskets, one for each heater side. This item is called a gasket o-ring, because, it is a gasket and o-ring built into one piece. This helps to assure a tight drip free seal every time. Measurements Inner Diameter: 2-1/8" Outer Diameter: 2-15/16"
Posted by Chuck Irvin on Oct 30th 2015
While ordering a 2" half-nut coupler, I became convinced that I needed to order this seal, as a better designed seal. Because I had trouble getting the new coupler to not "pop off", I tried one time the seal that came with the replacement coupler, I used the seal included plus Teflon tape on the threads of the male PVC pipe and the combination finally tightened down enough to prevent leaking in the joint. So, I didn't really need this product after all.
All prices are in USD.