I have an old cast iron bath tub with a lift and turn cover.

If I fill up the tub water is draining slower then expected. I am guessing hair.

I removed the metal knob on top of the lift and turn cover, and see a recessed square shape behind that. I assume there is a square shaped wrench that is needed to remove that cover so I can put a small 1/4" snake down there and clear it.

Or can I just open the overflow cover and snake that? I assume if it's hair it would be in the drain under the lift and turn cover BEFORE it meets the overflow tube, right?

snake thru the overflow cover.
you can use a small wire to clean away any hair at the lift cover.

It could be either or both possibilities.

I will try the overflow snaking this weekend.

But just in case I need to remove the lift and turn cover, what kind of a tool do I need for removing that with a recessed square hole around 3/8"X3/8"? Is this a special tool?

I removed the tub drain cover.

Turns out I didn't need any special tools. A flat head screw driver wedged into the square hole turned it loose.

There were lots of junk clogging the piece with the X underneath. Some hair, but most of it is actually strips of silicone caulk. I think the guy I hired to refinish the tub scrapped off caulk along the tub/wall joints and rinsed the loose pieces off the tub into the drain.