Come and see our amazing products! This small ball can generate huge power and do more workout than you think it could be for your forearm.This gyro ball correspond to 50 dumbbells of different weights. Control the speed and power with your hand, 10,000 rotational speed per minute could generate about 35 lbs weight. This new model start with internal pre-tensioner,no starter cords required.Just push to the inner ball and move your thumbs along the arrows direction to start,which make it more convenient. Pls confirm further with us if any query about packing info, inventory status and time schedule.