Rust streaks observed under the fifth wheel bolts are most commonly caused by which issue?

• A. Over-tightening
• B. Improper lubrication
• C. Corrosion from moisture
• D. Incorrect fastener selection

Answer: (D)

Rust streaks under the bolts point to corrosion at the fastener interface, and the most likely root cause is using the wrong fastener for that location. When the material, coating, or grade isn’t appropriate for exterior, load-bearing trailer hardware, moisture (and road salt) can attack the fastener more quickly. The result is corrosion forming around the bolt shanks and threads, which shows up as rust streaks as moisture wicks along the joint. Using the correct corrosion-resistant fasteners with the proper coating and torque helps prevent these streaks.