It's a dooamahefer. Don't leave home without it. Some one put that there to make you pay more for the shipping weight.
Actually I think Der's response was better than mine.
I had a screw in a plastic bag for 3 years before I found out it belonged to a bass pedal. The pedal works better now for some reason it's tighter.
It's a good thing too, I thought it had fallen out of my head. But nothing rattled. That's how I knew it wasn't mine.