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This is a Jesus nut – what kind of part is that? Why does it have such a bizarre name?

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Posted March 27, 2018

Imagine a small part of any mechanism that is so important, that its failure would bring entire thing to a catastrophic stop. How would you call it? Some soldiers with a good sense of humour named one such part a “Jesus nut” or “Jesus pin”. What is that part? Why did people name it like that?

Jesus nut is very small, but very strong. This one is from a Bell 222U. Image credit: Alan Radecki via Wikimedia

Jesus nut is a fist-size steel part from a certain type of aircraft. Aviation has a ton of its own unique technical words, but this one if a little bit different. It is widely used in literature, but it was created back in the times of the Vietnam War. The name was so fitting and the part is so important that later it became a good way to pay respect to retired officers. So what is it?

Jesus nut is quite literally just that – a nut. The importance comes from its place in the helicopter – Jesus nut is responsible for holding the main rotor to the mast. Technical name of the Jesus nut is the main rotor retaining nut, but where is the fun in that. While exact author of the term is unknown, it is believed to have originated during the Vietnam War. The legend says that one soldier asked an aircraft mechanic what is that thing and what would happen if it fell off during a flight. The answer was simple – “pray to Jesus”. You would also be screaming “oh Jesus” at that point, because failure of the Jesus nut would mean that the main rotor is coming off. Without it the helicopter cannot fly at all and will just plummet down uncontrollably like a brick. However, such catastrophes are incredibly rare.

Bell 222U – it still uses a Jesus nut, but some newer helicopter models use different methods of holding the main rotor. Image credit: Meggar via Wikimedia(CC BY-SA 3.0)

Jesus nut was mentioned in several books about experiences during the Vietnam War (for example, in “Chickenhawk” by Robert Mason). It even made its way into technical literature – people know very well now what is Jesus nut. Eventually it became a present to retiring military personnel. Because Jesus nut is such a crucial part of the helicopter, it became a symbol of respect.

Now a lot of modern helicopters don’t have a Jesus nut. There are many other different methods of fixing the main rotor to the mast. However, the name is not going to disappear, because people are already using it for other crucial components of other mechanisms. For example, there is a different Jesus nut in rock-climbing equipment – it first piece of protection placed on a pitch.

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