Poor fuel mileage

Danny I think what you refer to is a ball race these are used in conjunction with a block behind the king pin on the trailer the pivot of the trailer is all within the ball bearings and the 5th wheel stays in the same position on the trailer. These can be pinned and made ridged and used the same as an ordinary friction plate depending on what trailers are being pulled its more company preference theses days than any operating benifits

 

I've seen an anti jacknife system in the US that was similar, Apgar in Bound Brook used to have them on their tanker fleet. Looked real strange when bobtailing!