What is this piece called and how does it work?

[mike733]

My bathroom sink faucet is loose, and I want to lift the entire thing from the top to make sure there is no damage/mold/etc. from the previous owner. When I took a look underneath, instead of a faucet rosette, there is something anchoring it in the middle (picture attached). What is the piece of called, and how do I remove it?

 

[Mr_David]

Looks like the end of a toggle bolt.
I have never seen one like this but It looks like it was designed to just drop in from the top . I would disconnect the rod coming down through the hole from the pop-up drain assembly and pull it out. then look dpown into the hole from the top and see if it looks like maybe an allen wrench would fit into the hole.
I'll bet there is something you can turn from the top to tighten/lossen it.

 

[mike733]

Thanks, Mr_David!