I knew that stupid coupling between the copper heater pipe and the PVC was going to be a problem.

Home Depot, Lowe's, and Ace Hardware do not have a fitting that fits that collar. The guy at Lowe's insisted it was NPT threads even though it's 9 threads per inch and NPT is 11-1/2 (and why would you have tapered threads on a coupling?). I tried anyway and the collar does not thread onto the 2-inch NPT fitting he sold me.

9 threads per inch.
I tried looking at the unions and couplings and nothing available in the stores fit. The 1-1/2 inch repair couplings came the closest, but they were too large. The 1 inch repair couplings were too small.
Does anybody know what kind of fitting has 9 threads per inch on 2-inch pipe?

Home Depot, Lowe's, and Ace Hardware do not have a fitting that fits that collar. The guy at Lowe's insisted it was NPT threads even though it's 9 threads per inch and NPT is 11-1/2 (and why would you have tapered threads on a coupling?). I tried anyway and the collar does not thread onto the 2-inch NPT fitting he sold me.

9 threads per inch.
I tried looking at the unions and couplings and nothing available in the stores fit. The 1-1/2 inch repair couplings came the closest, but they were too large. The 1 inch repair couplings were too small.
Does anybody know what kind of fitting has 9 threads per inch on 2-inch pipe?