[wctekkk]

i believe it's 2 1/2 you might want to take the c/o cap w/you to plumbing supply dealer don't know where your at, like a Ferguson,Cal steam i do not think you'll find it at H/D or LWS . Maybe a schedule 80 male adaptor

 

[TheEplumber]

I have a 3 inch cast iron y fitting coming out of my basement floor. the top of the y has a clean out. the opening measures 2 7/8 " I want to add another 1 1/2" drain line to this. My initial plan was to get an abs male threaded coupling, attach it, add another y fitting with clean out ontop. Problem is...a 3 inch abs male coupling is to large to thread into this cast iron.

Any ideas? would copper/brass fitting work due to the thinner material?

Thanks,
Josh

You need to remove the CO fitting and use a rubber doughnut (tyseal gasket) to attach a new wye and clean out. You won't find a male adapter to fit your clean out

 

[Nailbags]

Buy a hub-less connector they are black flexible rubber and you tighten them with the hose clamps that come with them very easy and cheap.