The Grip-n-Rip Knob Stacker Choke-Up is designed to stack perfectly with each other. Create a more comfortable batting experience for your young player when teaching them to hit. The exposed side of the Knob Stacker mates perfectly with any other Grip-n-Rip Product and they stack perfectly together when more than one Knob Stacker is used. The under side of the Knob Stacker is relieved of material to aid in vibration dampening for mis-hits and aid in not impacting the moment of inertia to much. It easily stretches over the knob for easy installation.