The big nut

Over the past few weeks I have been acquiring a set of wire wheels for my MGB. Unlike the current wheels that have the standard four lug nut arrangement keeping them on the car wire wheels a single nut at the center of the wheel like race car wheels.

This arrangement was the cause of some concern. What if the nut comes undone? The wheels are spinning after all and nuts do have a habbit of working loose.

As I started reading up on how to fit the wire wheels I discovered that my concern was somewhat misplaced. The nuts that are visible simply hold the wheel to the hub and the brake assembly. If the visible nuts held the wheel to the car chasis there would be no way for it to turn.

So what holds the hub to the axles? A single medium sized nut hidden underneath a grease cap which is covered by the hub cap. So should I be less worried because this arrangement demonstrates that one nut is adequate or more worried because I now know that there are two single points of failure rather than one?