The pro 4 rear hub qr axle from hope is the benchmark for a disc compatible rear hubs with hopes proven reputation for bullet proof quality you have the security that this will be the heart of a strong and reliable wheel it runs on sealed stainless steel cartridge bearings with a qr axle and a 4 pawl ratchet system with 44 tooth engagement for near instant power transfer the hub shell is machined from forged aluminium billet with standard 6 bolt disc mount and a large diameter flange availab