The Hitting Jack-It is a complete hitting training system with patent pending design. The 5 oz size develops bat speed and works fast twitch muscles. The 9 oz size strengths hands and forearms, and improves muscle memory. The 12 oz size develops power. The Hitting Jackit works with all baseball and softball bats allowing players to develop during live batting practice sessions and off hitting tees. All current weighted products on the market are placed on the barrel of the bat causing a "casting" elongated swing, slowing down your swing, causing less power, and do not let you practice with live pitching. The Hitting Jack-it was developed as a complete hitting system by ball players for ball players to provide immediate results, quickly develop bat speed and power, and force your hands to work properly creating improved technique.