Park Tool DERAILLEUR ALIGNMENT GAUGE DAG-2.2
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"+.
DAG-2.2 FEATURES
- Compatible with 16" to 29"+ wheels (ISO/ETRTO rim sizes from 317 to 630+)
- Fits most frame/hanger combos including low clearance thru-axle derailleur hangers
- Length: 405 mm (16")
- Weight: 937 g (33 oz.)
https://www.parktool.com/en-us/product/derailleur-hanger-alignment-gauge-dag-2-2?category=Derailleurs+%26+Shifting#tabbed-section