Aviation Structural Mechanic (AM) Strand Practice Exam

Lock washers and lock nuts are used to resist loosening that comes from vibration and cyclic loading. In service, fasteners experience repeated fluctuations in load and continuous shaking, which can cause a bolt to turn slightly and back off, reducing the clamping force over time. Locking devices add friction or mechanical interference so the fastener resists turning despite these conditions. Lock washers bite into the surface or deform to increase friction, while prevailing-torque or other lock nuts maintain a resisting torque that helps keep the preload from relaxing. This helps keep joints tight and prevents loosening that could compromise the structure. They aren’t primarily for sealing joints, reducing weight, or improving corrosion resistance—their main role is maintaining clamp force under vibration and cyclic stress.