To facilitate the assembly of upper shells (back holes) for KJ-XR3 and KJ-Pro7 models in sizes L and XL, you can find specific hardware available. This hardware set includes 2 bolts and 2 washers, designed to securely fasten the upper shells to the rest of the shoe structure. It ensures a reliable and sturdy connection, allowing you to enjoy the full benefits of your Kangoo Jumps rebound shoes. It's worth noting that this hardware is also suitable for use with former models, ensuring compatibility and ease of use across different generations of Kangoo Jumps products.