Simple and effective batter's training aid for developing bat speed and arm strength. Excellent tool for warming up before taking the batter's box. Cast iron bat weights are durable and color-coordinated according to their respective weight. Can be used on bats with diameter of 2-1/8" or larger. Vinyl coated bat weight won't damage bats when properly used. For training only and not to be used for hitting or batting practice. For players of all ages and levels. Gradually build strength and competency according to your level; from youth ballplayers to players with biceps bigger than most youth ballplayers