Composite bat using carbon and duralumin. - Brand: ZETT - Model Name: Android II - Material: Carbon × Duralumin - Model Number: BCT21904 - Size: 84cm 67DIA. This is a composite bat made of carbon and duralumin. Composite bats can be used in official games for Little Senior, but I think they are not allowed for Boys. Of course, it can be used for practice. For sixth-grade elementary school players who will start junior high school hardball baseball next spring, we recommend getting used to it before purchasing a new one. Thank you for viewing.