I have a '68 C20 factory dually and all six wheels are hub piloted; ie, the lug nuts only hold on the wheels, the hub centers them up. The rear wheel lugs are obviously longer to accomodate the double wheels. The front hub has an additional casted piece that bolts to the drum that offsets the wheel outward. As Hotrod Lincoln mentioned, the outer front wheel bearing is mounted in the extension otherwise, there would be a tremendous load on the wheel bearings. All six wheels are identical and are flat-faced in way of the lug nuts allowing any two to be mounted back to back without the tires rubbing which means a pretty significant back-space to allow this to happen. (This is also the reason for the additional cast piece on the front because with the required back space the correct tire would hit the frame in a modest turn.)
