Removing a Watco Bath Tub Drain

I have a Watco bathtub drain. I do not know how old it is, because it was here when we moved into the house a year ago. It is metal, with a rubber seal at the base, it also has a small metal knob on the top. I am able to screw off the top. Iinside below the metal ball I see I small square metal tube inside a the circle. I have no idea how to get this thing off and need to clean out the hair from bathing my dog... it is stopped up. Please help. I have tried turning it clock wise and counter clock wise in the upright position (the position that enables water to drain) but it does not seem able to come all the way out. This is my first posting so if I am in the wrong forum I am very sorry.

Thank,
Erica

I can't remember which is which with those drains...
Some have a screwdriver slot under that knob you unscrewed...
Others you close then turn...
The close and turn maybe the one you have.
Good luck with the dog hair!
You may want to get a zip it.http://www.zipitclean.com