Why are lightweight steel bushings sometimes used in wooden structures?

Lightweight steel bushings are used in wooden structures primarily to prevent the wood from being crushed when bolts are tightened. In applications where fasteners are used to secure parts of a wooden structure, the compression of wood fibers can lead to damage, such as crushing or splitting, especially when high torque is applied. The steel bushings act as a reinforcing sleeve that distributes the load over a larger area and provides a stable surface for the fasteners. This reduces the risk of structural failure and prolongs the integrity of the wood by allowing for proper fastening without compromising the material.

The other options do not accurately capture the primary function of bushings in this context, focusing instead on aspects like aesthetics, weight implications, and friction, which are secondary considerations compared to the critical protective role of the bushings in maintaining the strength and durability of the wooden structure.