||This article contains weasel words: vague phrasing that often accompanies biased or unverifiable information. (February 2012)|
Jesus nut or Jesus pin is the main rotor retaining nut  that holds the main rotor to the mast of some helicopters, such as the UH-1 Iroquois helicopter; or more generally is any component which 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 rotors 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.
In literature the term Jesus Nut was used in Chickenhawk by Robert Mason, a narrative about his experiences in the Vietnam War. A Jesus Nut figures prominently in the climax of Clark McCann’s thriller Black Air.
Mountain bikers often use the term to describe the screw that holds the rear wheel pivot bar in place on a rear suspension bike. This bar holds the back suspension onto the frame of the bike. If the screw falls out, the pivot bar tends to slide out, leading to catastrophic rear-wheel failure, ending in unavoidable loss of the back wheel. Since the pivot bar will only come out under heavy vibrations, it tends to fail at high speed, therefore leading to serious injury.
Another use for the term is found in rock climbing, in which it refers to the first piece of protection placed on a pitch. This piece must be placed to resist an outward pull as well as a downward pull in order to avoid the possibility of a "zipper", in which the outward pull on the rope from the belayer arresting a falling climber pulls protection pieces from the bottom up. In addition, the Jesus Nut prevents the possibility of a factor two fall onto the belay anchor.
Jesus nut is also used in reference to the nut on the front of the recoil mechanism on some artillery pieces. Should this nut fail, the gun tube will come out of battery upon firing, potentially leading to death for the gun crew.
- Aviation Safety Maintainer 1/2002: Fatigue and Complacency - A Potentially Sorrowful Mixture Transport Canada
- Amazon.com: Black Air (9781612960036): Clark McCann: Books
- The Rattler/Firebird Jesus Nut Award
- Long, John and Gaines, Bob (2006). "Climbing Anchors, 2nd Edition". Falcon Press, London. ISBN 0-7627-2326-2.