Tennis ball trainer for juniors, with adjustable rebound force. - Brand: CALFLEX - Model: TT-31 - Application: Junior Tennis Trainer - Features: Ball rebound force changes Number of uses: About 3 times, so I think it's clean. It was a little difficult for my child, so I didn't use it much. I think it's also good for adults who are starting tennis. Product Description: Sakurai Trading (SAKURAI) CALFLEX Tennis Junior Hard Tennis Trainer TT-31 Ball material: Natural rubber String material: Rubber, nylon Base material: Steel String length: 590cm Product Description The "Hard Tennis Trainer TT-11" is a hard-type tennis trainer. It uses a non-pressure ball that does not change the ball's rebound force. With a newly designed string that combines nylon and rubber strings, the ball returns naturally. Comes with one hard tennis ball and one base. Materials Rubber, nylon, steel From: A tennis trainer that provides a ball return close to actual play with a combination of nylon and rubber strings. An item that allows you to practice alone even where you can't hit against a wall. The string length is approximately 5.9m.