Where can I find a Cast iron tub drain to fit a 2 5/8 " opening? The tub at the opening is about 1/4" to 1/2 " thick and is tapered downward in the opening.

I went and measured the drain in my old footed CI tub. It is a regular drain assembly that measures 2 5/8 and is hooked up to a 1 1/2" PVC drain pipe. Looks like a standard fitting. Where are you measuring the 2 5/8?

The actual opening is 2 5/8"

The opening itself is 2 5/58"

Mine must be a little smaller. It's getting harder to find old parts unless you live in an old city and befriend a packrat. I've adapted some of these by cutting rubber rings from heavy truck inner tubes. Put a good silicone bead under and above the ring, compress it between the strainer and the tub body. There isn't much static pressure in the drain so it doesn't take much to make a seal. You can also buy a small piece of shower base liner and cut one from that. HD and Lowe's carry liner.

Ok. Thanks for trying to help.