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 Share on Facebook (Opens in new window) Facebook Share on X (Opens in new window) X Share on Reddit (Opens in new window) Reddit Share on Pinterest (Opens in new window) Pinterest Share on LinkedIn (Opens in new window) LinkedIn