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.