I am selling this item as I haven't used it much. Rubber shows no significant deterioration (some minor cracks). No issues with use. It's sold on Rakuten and Amazon for prices ranging from 7,300 to 11,500 yen. Please refer to the size chart and level chart on the second image. As someone with swimming experience, I feel that even GREEN is suitable for junior high school students to adults (depending on swimming ability) for land training! The rubber is more durable than cheaper ones, so it doesn't wear out easily! Product Description StrechCordz Stretch Cord (with Paddles) Swimming Training Equipment Tension: 3.6kg ~ 10.8kg Color: GREEN For swimming land training. This is a muscle training tube with paddles. Because the tube has paddles, it fits perfectly in the palm of your hand, allowing you to train with movements similar to those in the water, and you can customize your training. How about using it for stroke strengthening and improvement, and land training on days you can't go to the pool or on your days off?