There is an O-ring that seals the outer hub assembly to the Ford wheel hub. On older Ford 3/4-ton axles (which is what this hub was designed for) there is a flange machined into the end of the wheel hub for the O-ring to seal against. The Super Duty wheel hub doesn't have this flange. The O-ring must seal against the two Warn snap-rings installed earlier. This isn't the smoothest sealing surface. We greased the O-ring well before installing the outer hub assembly. If water or dirt gets past the O-ring, it will only contaminate the locking hub mechanicals. The wheel bearings are still sealed from the hub cavity on a Super Duty, unlike on the older trucks. So far, with lots of winter use, nothing has gotten into Jane's new hubs.