sentences:  Merchants, manufacturers and businesses in every industry clamored for a semi-trailer and the shuttle concept introduced by Fruehauf using one tractor truck and 2 or more semi-trailers.Fruehauf used the Martin Rocking 5th Wheel up until at least 1919.Early that year, the manual coupler was introduced to the industry by Fruehauf and the jacks acting as front supports for the semi-trailer were supplanted by wheels, raised and lowered manually.