Where does this spring belong

I found a spring after removing the fan for my late 2012 Mac mini. The only springs I could find online pertains only to the ones for the heat sink. I did not nor have I ever removed/replaced the heat sink of my MM. So where did the spring come from?

Another question is why doesn't the screw for the fan/cowling come off? It comes off the motherboard fine but it's stuck holding the cowling and fan together? Thanks.