Material: TPRSize: The diameter of the hedgehog ball is about 6.5CM; the rugby ball is about 6*6*9CM. 11. 2 Hardness levels: There are 2 ranges for the grip ball, 4.5kg/10lb for rugby and 9kg/20lb for a hedgehog ball. It is used for grip training and rehabilitation. You can train alone or let your family and friends participate in the training. 22. Significant effect: The soft shoe spike design increases comfort and training effect. It is very suitable for rehabilitation exercises. The hand is strengthened. You can put the rope on your wrist to prevent the massage ball from slipping off during training. 33. High-quality and durable: The grip ball is made of high-quality rubber (TPR), which can maintain its shape even when used frequently. All fingers can be trained at the same time, durable and safe. It can be rinsed with water after use. 44. Excellent choice: The hand muscle trainer is light in weight and easy to carry. It can also reduce numbness and pressure on the hands, and is an excellent choice to prevent tension and relieve stress. 55. Perfect gift: The massage training set is a perfect gift for yourself, family, or friends for birthdays, Christmas, Valentine's Day, anniversaries, Mother's Day, and Father's Day.