*The size of the four balls used should be relational to the size of the cardboard used. For example, if you use two pieces of 8.5″ x 11″ cardboard for the shake table, use four 1″ in diameter bouncy balls. If you use two pieces of 12″ x 16″ cardboard, use four golf balls. If you use two pieces of 18″ x 24″ cardboard, use four tennis balls.