ALUMINIUM DERAILLEUR HANGER ALIGNMENT GAUGE PARK TOOL DAG-3

The Park Tool DAG-3 is the all-new derailleur hanger alignment gauge, engineered to be light, accurate and versatile. An alignment gauge is essential for diagnosing and repairing bent or misaligned derailleur hangers, often the source of shifting problems.

The long, precision-extruded aluminium body is built to tight tolerances and provides ample leverage for making adjustments. The sliding indicator measures alignment against rims of any size and rotates out of the way to clear seat stays, racks and other obstacles, allowing 360° measurement. The M10 threaded tip is replaceable and the gauge also fits low-clearance thru-axle hangers and Shimano Direct Mount hangers.

How to align a derailleur hanger with the DAG-3

• Mount the bike in a repair stand with the wheels level and check that the rear wheel is properly seated in the frame.
• Remove the rear derailleur and thread the gauge onto the hanger; if the threads are damaged, chase them first with the Park Tool TAP-10.
• Set the indicator against the rim at 3 o'clock, then rotate gauge and valve to 9 o'clock: with a gap under 3 mm the hanger is horizontally aligned.
• If the gap exceeds 3 mm, bend the hanger by half the gap, in small increments, rechecking both sides.
• Repeat the vertical check between 6 and 12 o'clock: the hanger is aligned when three points 90° apart are all within 3 mm.
• If fenders, racks or stays get in the way, simply pivot the indicator to clear the obstacle.

Why choose Park Tool DAG-3

• Extruded aluminium body: 645 g for a length of 420 mm
• Sliding, rotating indicator for 360° measurement even with racks and fenders
• Compatible with 16" to 29"+ wheels (ISO/ETRTO rims 317 to 630+)
• Replaceable M10 threaded tip
• Fits low-clearance thru-axle and Shimano Direct Mount hangers

After alignment always recheck the limit screws and derailleur indexing; a hanger bent several times that fails during correction must be replaced. For a light and complete tool, the Park Tool DAG-3 aluminium derailleur hanger alignment gauge is the most advanced choice.