Amazon.com: Derailleur Hanger Alignment Gauge - Simple to Use Measuring Straightening Convenient Fast Solve The Shift Problem - Fits Mountain Bike Rear Lifting Lug : Sports & Outdoors
Super B Derailleur Hanger Alignment Gauge (Silver) - Performance Bicycle
How to Align a Derailleur Hanger Using the DAG-2.2 - YouTube
DAG-1 Derailleur Hanger Alignment Gauge | Park Tool