Where are these hooking up to the system, a photo or two of that would help.
Most PVC used in pools is stock off the shelf stuff from the big box stores, but that part with the "O" ring probably is not. Specialty parts may need to be obtained from the manufacturer of the equipment it attaches to. I'm going to go,out on a limb and guess the O ring part is a hook up to the heater???
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I do my research and then check Amazon. Looks to me like a coupling. Not sure of size. These are ones I use:
Amazon.com : Hayward SP14982S 2-Inch Socket White PVC Flush Female Socket Union : Swimming Pool Heaters : Patio, Lawn Garden
I agree with previous post. A picture of where theses actually are connected would be great.
They are not couplings, they are unions. But, I agree with Tim in that you will likely have to get them from the equipment manufacturer as they often use proprietary threads.
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As mentioned, those parts are part of the unions that connect to their respective equipment. It would help if you could post pictures of the equipment to which they attach.
The top picture (black plastic) looks to be made by Hayward, but I'm not 100% sure.
The bottom picture shows an old union tail piece made by PacFab, now Pentair. The part number for the union kit is 271096. Search and you'll find them still available - picture below.
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