Why are lightweight steel bushings sometimes used in wooden structures?

• A. To prevent wood from being crushed when bolts are tightened.
• B. To prevent rust on bolts.
• C. To align holes precisely.
• D. To increase the hardness of the bolt.

Answer: (D)

When a bolt is tightened in wood, the surrounding fibers can crush or gouge under the load. A lightweight steel bushing provides a hard, smooth bearing surface that distributes the clamping force over a larger area of the wood, lowering the contact stress and helping prevent the wood from crushing around the hole. This bearing surface also reduces wear on the wood and helps keep the bolt aligned as it’s tightened.

Other options aren’t the primary reason for using bushings here. The bushing isn’t primarily about rust prevention, since that depends on coatings or bolt material, not the bearing surface. While bushings can aid alignment, that’s a secondary benefit. And the bushing doesn’t change the bolt’s hardness—hardness is a material property of the bolt, not something the bushing alters.