Park Tool Derailleur Hanger Alignment Gauge DAG-3 Black ■ Length: 420mm Purchased new on Amazon in March of this year for around 20,000 yen, used only once. It really worked. (Result of the owner repairing a 29-inch MTB) - A gauge for checking and correcting the distortion of the derailleur hanger (dropout). - The most common cause of shifting problems is the distortion of this derailleur hanger. - Compatible with thru-axle derailleur hangers and Shimano direct mount derailleur hangers. - Attach this tool to the screw hole where the derailleur is mounted, rotate the gauge, and correct it so that the distance between the gauge and the wheel and rim side surfaces is uniform at multiple points. - The DAG-3 can measure and correct 360 degrees without catching on the seat stay, etc. - Release year/model year: 2021