so you are saying to reuse the one already in place attach this threaded drain to the existing one?
Not positive what L is selling. The bottom portion, washer, gasket and overflow cover and connector come in the box with the pictured part. You then glue your pipe to that, tee up for the overflow and reuse or add your trap.
the one you sent me is not avail in my local lowes store. can I use this one instead?
https://www.lowes.com/pd/Keeney-1-5-...-Drain/3132235
Never heard of or used it but I assume it would be okay. You might also check HD or do an SOS at Lowes.
Verify contents of any you purchase. You should do it with all new parts, plumber's putty under the drain (inside the tub) and then not have to mess with it for 30 years.
I like the Watco because the the stopper unscrews from the base making it easy fish out hairs with one of those flexible saw toothed snakes. The stopper replacement gaskets (once every 10 Years or so are easy to find and replace.