Jesus nut

Jesus nut, or Jesus pin, is a slang term for the main rotor retaining nut which holds the main rotor to the mast of some helicopters, such as the UH-1 Iroquois helicopter; or more generally is any component that represents a single point of failure with catastrophic consequences.
The term Jesus nut may have been coined by American soldiers in Vietnam; the Vietnam War was the first war to feature large numbers of soldiers riding in helicopters.
If the Jesus pin were to fail in flight, the helicopter would detach from the rotor and the only thing left for the crew to do would be to "pray to Jesus." Real examples of the Jesus pin failing are few and far between. However, the pin must be checked before the flight. Some more recent helicopter systems do not have a Jesus nut.