<P> 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 coupling consists of a kingpin , a 2 - or - 3 ⁄ - inch - diameter ( 50.8 or 88.9 mm ) vertical steel pin protruding from the bottom of the front of the semi-trailer , and a horseshoe - shaped coupling device called a fifth wheel on the rear of the towing vehicle . </P>
<P> 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 coupling consists of a kingpin , a 2 - or - 3 ⁄ - inch - diameter ( 50.8 or 88.9 mm ) vertical steel pin protruding from the bottom of the front of the semi-trailer , and a horseshoe - shaped coupling device called a fifth wheel on the rear of the towing vehicle . </P>
why is it called a 5th wheel trailer
why is it called a 5th wheel trailer
requiring the coupling to be installed in the bed of a pickup truck as a towing vehicle , and `` fifth wheel ''
requiring the coupling to be installed in the bed of a pickup truck as a towing vehicle , and `` fifth wheel ''