A misaligned derailleur hanger can cause skipping, missed shifts, and wreak general havoc on your bicycle's drivetrain. The DAG-2.2 is an indispensable shop tool that can be used to both measure and straighten misaligned derailleur hangers, diagnosing and solving many shifting problems. Compatible with virtually all derailleur-equipped bicycles, and adjusts to work with wheels from 16" to 29"+