Helicopters have a built-in nut which has a crucial function. It holds the main rotor to the mast of the helicopter. The slang term commonly used is the “Jesus Nut”; the technical name is the “main rotor retaining nut”. If this were to fail in flight, it would have catastrophic consequences!
Shortly after I had arrived on the field, the so-called TT straps (Tension Torsion Straps) on the helicopter needed to be replaced. On Bell helicopters these need to be replaced every three years, if they haven’t had to be replaced sooner due to the number of hours flown. First the main rotor needs to be removed from the helicopter, then the rotor blades are separated from the rotor head, which has to be disassembled, cleaned and inspected. The TT straps are used to attach the rotor blades to the rotor head. Then the rotor head and the rotor blades are aligned and the whole rotor is balanced before it is put back on the helicopter and fixed with the Jesus Nut. Another mechanic has to inspect the work before various tests are made: first static tests followed by hover tests and finally cruise tests.
According to Wikipedia, the name “Jesus Nut” may have been coined by American soldiers in Vietnam.
Daniel, helicopter mechanic