Kettler Adjustable Spring Grip Helps to condition and strengthen your hands, wrist and forearm muscles Ideal sports tool for tennis, bowling, golf and all your daily strength needs Triple steel tension coil build Strong plastic handles are textured and molded Ergonomic design to fit your hand for a better workout When use, you use single hand or both hands hold the hand grip tightly and strongly force the two handles to close up, then release You can repeat the exercise at home or gym, so easy