BOX Four Rear Derailleur - 8-Speed Medium Cage Black ModelNumber=E2131 Length (mm) 50 Material Aluminum

Length (mm) 50 Material Aluminum Defined Color Black Valve Core Fixed Valve Presta Med 41-55mm

Mirror technology inserts to provide additinal sit bone relief

Features Vent Valve Technology for super simple service if the need arises

7 Color Black Flange No Lock On Yes Weight 120 Grip Shift Specific No Defined Color Black Shape Round

Keep your hydration right between your arms and your computer at a glance

BOX Four Rear Derailleur - 8-Speed Medium Cage Black ModelNumber=E2131 Length (mm) 50 Material AluminumPrime 9 Technology for less derailleur travel and better chainline. Less wear and improved lifespan Box One features: Adjustable Tri Pack limited slip clutch, forged inner and outer cage, Pivot Tech cable stay, sealed bearing pulleys and 3D forged linkages Box Two features: Tri Pack limited slip clutch, forged inner and outer cage, Pivot Tech cable stay, sealed bushing pulleys and 3D forged linkages Box Three features: Limited Slip Clutch, stamped