The spacers are plastic and that looks metal to me. Is that a set screw as well?
If plastic = Spacer
If metal with a set screw = Since you said it came from the right side my though is it's from your cannon. Their are a couple of those as part of the cannon assembly but I could have sworn they were tied into brackets. It's been a long time since I messed with that assembly so I could be wrong but I would start there.