Home » Training » Trailer Glossary » Fifth Wheel Top Plate Fifth Wheel Top Plate A Fifth Wheel Top Plate is the top portion of a fifth wheel assembly that contacts a trailer’s bolster plate during the coupling process. It houses the locking mechanism that connects to a trailer’s kingpin Click to share on Facebook (Opens in new window)Click to share on X (Opens in new window)Click to share on Reddit (Opens in new window)Click to share on Pinterest (Opens in new window)Click to share on LinkedIn (Opens in new window)