Shimano slx rear mtb hub m678slx rear freehubs are designed for lightweight and durability the micro ratchet freehub mechanism xtr saint dura ace offer super quick engagement for added acceleration shimanos proven angular contact cup cone bearing system provides trouble free performance and easy servicing featuresdurable construction for a longer maintenance cycleangular contact cup and cone bearing with grease sleeve ensures smooth running even in muddy conditionsexcellent stiffness