The purpose of the cable ball is to counter balance the weight of the cable on the opposite side of the top pulley. Nothing to do with "whipping" around, that is the 'tag' man's job. More cable, more counterweight is needed. A 20 pound ball, plus the weight of the blocks, clevises, hooks and chokers would counter balance a lot of cable-weight. This looks to me like a vintage headache ball because the modern ones are made in two pieces. Reason for that is simple, you can change them out, (larger or smaller), without removing the other fittings. The taller the rig, the bigger the ball. A wrecking ball is a totally different thing, 20 pounds is not gonna do much, I'm certain It's not a wrecking ball.You know I thought of cranes as I worked with them on the rail road but for some reason kept thinking wrecking ball which are like 1500 + lbs. But we did have round weights on boom cranes and cherry pickers above the hook for moving rail and timbers. Keep it from whipping around.