evo.com | Industry Nine Hubs > They're going to have to get used to it. The sound. With nearly 700 audible clicks per revolution, your Industry Nine Hydra Classic ISO 6B Boost XD Rear Hub makes a telltale buzz that can injure fragile eardrums. Tough luck, tenderberries, this is the sound of dependability, longevity, and bomber construction. We love the sound of instant engagement in the morning! This model is for use with SRAM XD cassettes. A2 Tool Steel Pawls and Driverings 0.52deg Engagement 6 Bolt Rotor Compatible 7075-T6 Aluminum Alloy 12 x 148mm Boost Spacing | Industry Nine Hydra Classic ISO 6B Boost XD Rear Hub 2023 - 12x148 XD / 32Hole in Blue | Aluminum