the present invention relates to a tractor for transferring a variety of trailers and transfer devices equipped with a kingpin , which tractor is equipped with a vertically adjustable 5th wheel . the 5th wheel comprises gripping members and power mechanisms by means of which the transfer device is by the kingpin with a convenient force pulled into contact with the 5th wheel 4 thus making an inner force balance of the joint 4 - 12 possible .