Shimano TL-RD10 is a tool designed to adjust the parallelism of the rear derailleur mount and hub axle lock of the rear dropout. It includes a gauge for easy use and quick adjustments. The tool helps to align the rear derailleur hanger and the hub axle, ensuring smooth and precise shifting performance. It is compatible with various hub types, including SHIMANO DURA-ACE, SHIMANO 600, and Campagnolo hubs.