Part one of a new series of threads in which you help me fix something in my flat.

Today: the case of the mysterious encased toilet seat fixtures.

My toilet seat is loose on one side. I tried to tighten it but it just keeps on turning forever not getting tighter. I thought I'd need a new toilet seat but what's this?! There's no underneath bit where the screw comes out of, it's all encased internally in my toilet. What the sweet dee is this? How do I deal with it? It's been confusing me for a very long time...