Fifth Wheel 3 : The semi-circular coupling device mounted horizontally on the back of a tractor which engages and locks with a trailer allowing the trailer to pivot and turn
Association of Marine Underwriters of San Francisco (AMUSF), Glossary of Marine Insurance and Shipping Terms, http://www.amusf.com/Definitions_A.htm, CA, USA 2011. (Mrtm Insur and Shipping - Amer) {575}