coupling pole

plural coupling poles

1. A connecting piece between the front and back axles of a wagon or trailer, often equipped with pins for extending or shortening the bed.

   It is equipped with a brake and is extensible on its long coupling pole, extending from axle to axle.

   2013, Henry C. Mercer, Ancient Carpenters' Tools, →ISBN, page 39

   1 more example

   I don't remember much of anything else happening other than us going to town, and we would ride the coupling pole of the wagon that stuck out in the back.

   2014, Doyle W. Williams, My Mother's Branch:The Lineage and Life of Carrie Viola Reeves and Her Family, →ISBN, page 264