I'm considering replacing my shower/tub faucet. I was trying to remove it and saw this. I attempted using a flathead screwdriver, because it looks like a big screw, but that ended up tearing a little chunk out. Is this holding the faucet onto the pipe? If so, what tool do I need to remove it? I tried simply twisting the faucet off, but it didn't budge, and until I'm 100% positive it twists off, I don't want to try turning any harder than I have.