headache ball
n.— «Headache ball: The large, round, steel ball weighing 500 to 1,000 pounds that hangs from the end of a construction crane’s cable. It has a hook on the bottom and is used to keep the cable from rolling back up on itself.» —“Chicago Speak” by Anne Keegan Chicago Tribune Feb. 3, 1994. (source: Double-Tongued Dictionary)