One of the best gimmicks ever created for predictions is the Swami Gimmick, or Nail Writer. Theoretically, the sky is the limit with such a gimmick, because it allows you to secretly make a "prediction" long after it is supposed to have been made, and after the outcome of the event predicted is known to you.
With just a modest amount of practice, it is possible to produce mind boggling effects with this simple gimmick. This is an adjustable gimmick, made of brass, to fit all thumbs and take various sizes of lead. Includes instructions.