There's a brass plate in the middle of the floor in our living room. We are assuming it's an electrical outlet but we cannot get it open. The slot is about an inch and a half in length but not very deep. There is a midpoint where it turns easily but if we turn it to the left or the right it tightens up. How do I open this darn thing!?

Post a picture. If it is a floor outlet cover, it should also have a regular screw inn the middle, like a wall outlet. Remove that. Otherwise, keep screwing counterclockwise, maybe with a bigger screwdriver.

I had a place with one. It probably isn't solid brass, and is rusted. Put a tiny drop of oil on the edge, maybe 2. Use something wider than a screwdriver, like a quarter.

Could be Network, Electrical, and or phone. May be other screws to remove whole cover. Blaster, or any lubricant should help, don't try too much force with too small a screwdriver to prevent deforming.

Could also be a latch arrangement.

Move the cover to it's loosest position (middle of arc) and see if the lifts off.