I currently have a cast iron pipe in my half bath that is currently used to "unplug" the pipes. This pipe sticks out of the floor about three inches. I want to find an adapter that would allow me to use the drain for a bathroom sink connection to PVC.

The problem with the current pipe is the corrosion and lots of it. There were internal threads. These threads are now a massive corrosion. The id of this mass is about 2.5" to about 2.75".

Any suggestions?

Thanks... Bonnie

Bonnie, sounds bad to me. If you have a pipe coming up out of your drain system, and it is open, it is allowing sewer gases to enter your home. This is not healthy. Yes you could get it converted with if nothing else a rubber boot connection that goes from the od of the pipe to the od of the new drain line.