There are several ball designs that fit your needs (and are commonly used for GBC machines) - a selection : * [LegoBall, Bionicle Zamor Sphere](https://www.bricklink.com/v2/catalog/catalogitem.page?P=54821), and their various multi-colored variants (eg. [Ball, Bionicle Zamor Sphere with Marbled Yellow Pattern](https://www.bricklink.com/v2/catalog/catalogitem.page?P=54821pb04)) (16.5 mm diamater) [![enter image description here][1]][1] [![enter image description here][2]][2] * [Ball, Sports Soccer Plain](https://www.bricklink.com/v2/catalog/catalogitem.page?P=x45), and their various multi-colored variants (eg. [Ball, Sports Soccer with Standard Pattern](https://www.bricklink.com/v2/catalog/catalogitem.page?P=x45pb03)) (17.9 mm diameter) [![enter image description here][3]][3] [![enter image description here][4]][4] * [Ball, Sports Basketball with Standard Black Lines Pattern](https://www.bricklink.com/v2/catalog/catalogitem.page?P=43702pb02) (14.2 mm diameter) [![enter image description here][5]][5] [1]: https://i.sstatic.net/x4Rh9.png [2]: https://i.sstatic.net/EP2fK.png [3]: https://i.sstatic.net/Y3k7D.png [4]: https://i.sstatic.net/8eezk.png [5]: https://i.sstatic.net/Ff9nW.png