[Tidybuoy]

Originally Posted by Porchdog

https://www.engineeringtoolbox.com/cast-iron-soil-pipe-dimensions-d_1751.html

I don't do much with cast iron, but I'm going to say that hub is 2" cast. See chart linked.

2" steel or PVC is 2-3/8" OD.

I don't know about Ferncos, but I'm guessing that you need a 2" x 2".

Sounds right. Now that I think about this, I previously did this with the main sewer line. But at the time, I ordered a 4" fernco and never measured the hub because I knew the pipe was 4" (might have actually been 6" but it's been so long, I don't remember and I'm not crawling under the house just for this conversation )