A replacement for the part of your sink that keeps water in! It's the threaded rod which lets you adjust the height of the plug, with the weird circular part and all! I do not know what that circular part is actually for, but it is there, and it works (I think. I don't know what its for, so I can't actually tell if it is doing what it should.. The plug works at least!)
I don't know if this is standard in other countries than Denmark, but I've seen it quite a lot here, and mine broke. So if anyone else has that problem, here you go!
Maybe use something else than PLA. It's not that great with the temperature fluctuations in the sink.