(A bicycle sprocket)
A sprocket may be useful for a bicycle but it can be a dangerous weapon if modified into the one shown in the photo.
A few days ago, a few students were caught by the school disciplinary teacher for a gang fight. During the investigation, the teacher discovered a few things that should not be in school at all such as, cigarettes and the sharp sprocket (Used as a weapon). The matter was brought up to the police and they were handed over to them. Well...that's my school. Hahaha...such a challenging school.