The present invention relates generally to trailer hitches and more particularly, to structures for adapting a trailer hitch to either a truck bed or an agricultural type tractor. 
An increasingly popular type of trailer is the so-called "goose-neck" trailer which connects with a trailer hitch located in the bed of a truck rather than the normal type of trailer which connects to the rear end of a towing vehicle.  One of the reasons for such an arrangement is to place the weight more centrally and above the wheels of the vehicle rather than rearwardly thereof.  This arrangement allows for much better control over the trailer when it is being towed and consequently allows the trailer to be of a much bigger variety than could be accommodated by a normal rear end hitch arrangement.  This popularized trailer hitch arrangement has been used for campers and for agricultural trailers, and it is to the agricultural type of trailer that this present invention is directed. 
An agricultural trailer of the type referred to above is extremely versatile, and a truck which would have this same capacity would cost a great deal more.  Furthermore, the upkeep on such a trailer would be much less.  In a typical farming operation of a few years ago, the equipment would include nearly always a pick-up truck and also a grain truck which could additionally be used to transport livestock from place to place.  With the use of the above described goose-neck type of trailer, only the smaller pick-up truck would be essential.  Additionally, the license fees for using a trailer of this type would be much less than the license fee for a large truck of the same capacity.  Consequently, it is because of the lower costs and its versatility that the goose-neck type of trailer has become so popular. 
There are several alternatives as to the type of hitch to be used for this type of trailer, and the two types which are most commonly used are the ball-type hitch and the conventional semi-trailer truck type of hitch.  Both types of hitches can, of course, be mounted to the bed of a pick-up truck.  The ball-type of hitch is less bulky and would be preferable for that reason; but, the semi-trailer truck type of hitch, such as that shown in the drawings herein, is preferable because of its automatic hitching feature and also because it is safer.  It is safer because of the large flat supporting surface which is used as contrasted from the small surface which is contacted with a ball-type hitch. 
It would be desirable, of course, to be able to use the conventional semi-trailer type of hitch and to be able to remove it from the pick-up bed when other uses of the pick-up truck are contemplated.  Also, it would be desirable to be able to also use an agricultural-type tractor to move the trailer from place to place, especially when the trailer is to be utilized for off road situations, such as when the trailer is used to unload grain from a grain harvesting combine in the field.