The brake drum is from a car.




But there's more: it is part of a braking system called (you may have guessed it) a drum brake. The drum is the part that the brake pads push out against, causing friction to stop the car. 
In musical terms, it is a percussion instrument often used as a sound effect in a manner similar to the tam-tam. The brake drum sounds quite a lot like an anvil, and is often used as a substitute when an orchestra cannot afford a blacksmith-in-residence. Brake drums are used notably in the percussion ensemble classic, "Double Music", composed by Lou Harrison and John Cage. If you ever replace your own brakes and want to make a couple bucks of scrap, don't hesitate to contact your local university's percussion studio, because there are never enough brake drums (see example below).