The Box Two Prime 9 X-Wide cassette is where Prime 9 began. Originally developed for E-MTBs to deliver long service life and a wide gear range with fewer gears, it quickly proved itself on unpowered MTBs as well. All cogs are stamped from steel, with the larger ones pinned to alloy spiders for added strength and durability. Due to its origins, it remains the most durable cassette in the range. Available in two versions, the standard 11-50T is suited for traditional MTB use, while the 12-50T E-Bike version features slightly adjusted gear spacing optimized to handle the unique torque and load demands of E-MTB riding, offering smoother power transfer and increased longevity. SUPPORT MATERIAL Prime 9 Technology™ View Prime 9 Drivetrain Compatibility Manual View Prime 9 Comparison Chart Why Prime 9? Please see page 6 of our guide for notes regarding the 2 HG drivers.