I'm trying to replace my kitchen sink faucet. The faucet is in the corner of the sink. I looked underneath the sink, where I expected to see a round nut which I would unscrew to release the fixture, I found an unusual triangular-shaped attachment. I have uploaded the picture I took. I'm not sure how to undo this fixture now, and I don't even know what to call it so I can't even look it up. Does anyone have any experience with this kind of faucet attachment?