There were a couple of topics about big trucks - and someone mentioned a "fifth wheel" - so thought some people might like to know what some of the terms were.
Also - (it's a stretch) - almost everything is transported at some point by truck - including our machines, fabrics, mail, etc.
Example: "fifth wheel" -
From the expression "so and so felt like a fifth wheel at the party . . . " I thought it meant something like a spare tire on a rim.
It isn't - it's that thing that looks like a horseshoe on the back of a tractor (front part of a truck) that a trailer hooks/locks into.