Jesus Nut is an unique part of helicopter. Its name came from the facts that it hold entire helicopter during flight and if it were to fail in flight, the only thing left to do would be to pray to Jesus.
That nut must transfer the entire weight of the helicopter from the main rotor shaft to the rotor. The teeth engage with the locking key, which holds the nut in place once it’s torqued down.
Many helicopters have a threaded mechanical fastener, a “nut”, at the top of the rotor that holds the rotor head down on the rotor mast. This is a very large nut that is tightened to very high torques and also safety wired with a number of anti-rotation devices so it cannot simply twist itself off. Because this nut is the primary retainer that holds the rotorhead in position and prevents it from flying off, helicopter pilots refer to it as the “Jesus nut” because if it is lost everything is lost. But Jesus nut failure’s is extremely rare. Never heard any event of jesus nut failure.