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A dictionary isn't much help for me in this case as I don't even know if there is an equivalent in my native tongue, so I don't know what to look for.

I have to describe what I mean:
Consider a truck pulling a trailer that only has an axle (or axles) at the back of the trailer. The front of such a trailer rests on a horizontal mount-plate located above the back-axle(s) of the truck.
This arrangement is also sometimes found on bigger model pickup-trucks to enable them to pull such trailers.

I don't mean the hook found at the back off a regular car to which you can hitch a trailer or caravan.
Or the heavy duty hitch arrangement to put a trailer (with axles front and back) after another trailer. (Also found sometimes at the back of lorries, tractors and some trucks.)

Is there a proper word (or phrase) for this mount-plate in English?

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  • Do you mean a semi-trailer and the cab of truck? Or a trailer and a pick-up truck?
    – Lambie
    Nov 20, 2017 at 16:07
  • The question seems unambiguous enough, but requires careful reading. It would be clearer if the distinguishing features (large flat horizontal plate, not merely a hook or a round ball such as used to pull smaller trailers) were placed in the first couple of lines of the question, rather than halfway into the second paragraph (for the plate) and the third paragraph (for "not a hook").
    – David K
    Nov 20, 2017 at 22:20

4 Answers 4

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It is called a fifth-wheel coupling:

The fifth-wheel coupling provides the link between a semi-trailer and the towing truck, tractor unit, leading trailer or dolly. Some camper trailers use a fifth-wheel configuration, requiring the coupling to be installed in the bed of a pickup truck as a towing vehicle, and "fifth wheel" is therefore sometimes used as a synonym for such campers in North America.

The term fifth wheel comes from a similar coupling used on four-wheel horse-drawn carriages and wagons. The device allowed the front axle assembly to pivot in the horizontal plane, to facilitate turning. Basically a wheel was placed on the rear frame section of the truck, which back then only had four wheels; this wheel that was placed on the frame was the "fifth wheel", hence the name. The trailer needed to be raised so that the trailer's pin would be able to drop into the central hole of the fifth wheel.

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Wikipedia: Fifth-wheel coupling

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5

The general term for the trailer attachment point would be the "trailer hitch", but that term is mostly reserved for trailers that are towed completely behind the truck.

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The attachment point on the semi-trailer is also called a "king pin". You'll sometimes see highway department signs limiting semi-trailer length to "x feet from king pin to rear axle."

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1

Also look into goose-neck. Very common and popular with pick-up trucks for hauling equipment trailers, house trailers, etc.

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