Grip Strength Training, 2-inch Piston Climbing and Pull-Up Holds EXTREME GRIP STRENGTH TRAINING - 2-inch diameter, 8-inch long solid cylinders for training extreme grip strength. Challenging for professional athletes, but still fun for kids! COMPATIBLE with Slackers brand Ninja Line for American Ninja Warrior training, gymnastics, rock climbing and Crossfit training. Also compatible with standard cable weight machines as an attachment. Used in the Ultimate Ninja Athlete Association (UNAA) competition and at professional Ninja gyms, Parkour gyms and Rock Climbing gyms throughout the country. LIGHTLY TEXTURED GRIP will not hurt your hands and allows for no-slip grip. Handcrafted and intended for indoor use. 100% Manufactured in the USA. Specifically the great state of Maine! Warrior Life Gear is the official brand of the Maine Warrior Gym.