Designed for working on your rear derailleur in the garage workshop the Park Tool Derailleur Clutch Adjustment Wrench features a dual-end design with 3 and 5. 5-millimeter wrench ends for adjusting the clutch tension of Shimano XT SLX Deore Saint and Zee Shadow Plus Rear Derailleurs as well as all previous Shadow Plus models. Ultimately this allows you to adjust the rear derailleur's clutch mechanism so you can reduce unwanted drivetrain noise and excess chain slap when you're riding over rugged trails.