There's a round part that's bolted on to the head, 3 lines in, one of them at least seemed to be fuel. No idea what the part is called, please help?

And if I take it off, does it have to go back on a certain way? Because there's a spring attached to it somehow where it pokes through a hole in the head.

Seriously dumb question probably but I swear I looked in the book all over the pages & couldn't figure out what it is. Thanks in advance!!! It's the little part with the tape on it.