Chris King hubs have two different axle designs, both unique to Chris King. The difference is in how bearing preload is set. The one-piece axle uses an adjusting clamp that lets you lock the axle into place against the bearing. The two-piece axle instead uses a doubly-threaded adjusting cone - once it is threaded correctly between the two, the two pieces of the axle tighten together to hold it in place. The only functional difference between the two otherwise is that the two-piece axle must be used with a skewer; the clamping force of the skewer is required to handle some forces across the axle. The one-piece axle can be used with the Chris King Fun Bolts instead of a skewer if preferred.
The overall design is based around using a large-diameter aluminum axle which necessitates handling stresses differently from a more traditional hub and axle.