When it's time to overhaul your Chris King mountain rear hub equipped with a Twin Bearing or Gen 4 axle system, this is the kit you need. Includes all the inner and outer seals, snap rings, and o-rings to get the hub back up and running. Fits the following hubs equipped with Twin Bearing or Gen 4 axle: Boost 6 Bolt Boost Centerlock Superboost Centerlock Superboost 6 Bolt Part number PHB592 If you have a Needle Bearing equipped rear hub, you'll need this kit