Thanks to all that provide answers, as they have been most helpful and I am hoping somebody might know of a way to help me with a small problem.

I am doing a restore on our main bathroom and one of the last items I wanted to replace was the tub/shower drain stop and replace it with a modern toe step drain stop.

It appears that they simply screw into place in the floor of the tub but the old one simply refuses to budge no matter how hard I try.

Is there a trick to this? Is it reverse threaded or does anybody know of an easier way to remove one of these pieces?