Jesus Nut

Jesus nut or Jesus pin are colloquialisms for the main rotor retaining nut that holds the main rotor to the mast of some helicopters, such as the UH-1 Iroquois helicopter. The term 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. Other sources suppose that the term may be coined as early as by Igor Sikorsky, a pioneer of rotor wing aircraft, who was a deeply religious person .

The term may have come from the idea that, if the Jesus pin were to fail in flight, the helicopter would detach from the rotors and the only thing left for the crew to do would be to pray to Jesus. In addition, A person must have faith in the Jesus bolt to do its intended job without failure. 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.

More recently, it has come to be a generic engineering term referring to any single component of a system whose failure would cause catastrophic failure of the whole system.