Even though most of the complaints come from the same 22-car fleet, different operators were behind the wheel when the cause of the complaints occurred. The concern is that the wheel studs could fracture, as the complaints allege happened, which could then lead to a wheel leaving the vehicle and, rather obviously, loss of control.
Though they certainly are not screws at all, you could think of the wheel studs as the "screws" to which lug nuts are attached to secure a wheel to the vehicle, and in this case, the Fusion has five wheel studs per wheel.
A full recall could involve some 280,000 vehicles, and Ford is reportedly cooperating with the agency to bring the situation to a resolution.
[Source: Detroit News]