The Box Four Rear Derailleur is the base of Prime 9 Technology that offers an affordable clutch based 1 by 8-speed derailleur that is simple and light; this makes it a perfect candidate for every entry-level bike that traditionally has a 3 by drive-train that is neither durable nor user friendly. SUPPORT MATERIAL Prime 9 Technology™ View Prime 9 Drivetrain Compatibility Manual How is the Ebike variant different? View Prime 9 Comparison Chart View Prime 9 E-Bike Comparison Chart Why Prime 9? References: Standard Mount vs. Direct Mount Derailleur Hangers