What is used to distribute pressure and relieve friction under nuts and bolts?

The correct answer is the washer, which is specifically designed to distribute pressure evenly under nuts and bolts. When a bolt is tightened, it exerts a force that can create high pressure in a localized area around the nut's contact surface. A washer acts as an intermediary between the bolt head or nut and the material being fastened. By providing a larger surface area, washers help to spread the load over a wider area, reducing the risk of damage to the material and preventing fatigue failure over time.

Additionally, washers serve as a barrier that reduces friction when tightening or loosening nuts and bolts, which can lead to smoother operations and improved torque application. They also protect the surface of the material from damage that could be caused by the edges of the nut or bolt.

The other options do not fulfill the same purpose. Nuts are fasteners that hold components together, lagging pads are used for vibration isolation and damping in specific applications, and flange shields are generally used to cover flanged connections and do not distribute pressure in the same way that washers do.