This drain has a cable operated stopper, controlled by turning the overflow unit about a half turn to seat the stopper... By looking under the tub I can see a large nut under the assembly but if this nut hold it in place I'm completely baffled as how they installed it as there is not sufficient clearance twixt the floor and the tub bottom to get a wrench in there let alone a hand.
Only ID of the tube brand or model is a decorative escutcheon on the lip of the tub inscribed ALMICO in large letters under which the words COMFORT and ELEGANCE follow in flowing script.
I would guess this tub to be 15 or 20 years old..
Any tips or suggestions would be much appreciated... Tthanks for your interest... CORNEY

Hi Corney...

If this is a typical cable operated unit (see the image) you'll need to remove the basket strainer (#11 in picture below) itself... it unscrews!

If there is a cross bar in the basket strainer you may be able to use two screwdrivers and insert them into the basket strainer and then crisscross them across each other and spin the basket strainer out. Alternatively, you could purchase a "tub-drain removal tool" (see image) and insert that into the basket strainer and unscrew the basket that way.