The attached pictures represent a 4 inch round steel lid of sorts, on the end of a steel pipe. This was from a shower, and what the shower drain drained into from the P-trap. I'm a novice, but is there a way to screw this off, any particular or specific tool I must use? Or, is this a "gotta call a plumber"? I am super and incredibly appreciative of any help, advice, thoughts, or insight, thank you!