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FIELD OF THE INVENTION 
   The invention relates generally to work vehicles such as tractors. More particularly, it relates to vehicle mounts or hitches for hitching other devices to such work vehicles. 
   BACKGROUND OF THE INVENTION 
   Vehicles such as tractors often need to be attached to implements. The implements may be towed on their own wheels or may be mounted in a fixed manner to the rear of the chassis or frame of the tractor. The former include wagons, carts, material spreaders, mowers and the like. The latter include pavement breakers, backhoe attachments, grading blades, ground breakers and plows, among other devices. 
   These different implements are affixed to the vehicle in different ways depending upon the desired flexibility and rigidity of the coupling between them. For a relatively rigid connection, such as for implements like plows or cultivators that need to be raised and lowered with some regularity, the chassis of frame of the vehicle is coupled to a three-point hitch assembly, which often includes an adjuster such as an adjustable eye or a hydraulic actuator that permit the hitch to be raised and lowered with respect to the vehicle&#39;s chassis. 
   Other implements such as wagons and carts can be coupled to the tractor simply by providing a bracket (or “drawbar”) with a hole through which a pin can be inserted. These couplings are used to connect the tongues of wagons or other vehicles that do not need the vertical or lateral support of the rigid frame or chassis of the tractor. 
   These two couplings—the drawbar and the three-point hitch, are the generic couplings provided on most modern tractors. This is not to say, however, that the rear structures of the chassis or frame to which these are mounted are the same. Each tractor may be manufactured differently, and may have different and unique structures at the rear of the chassis or frame. Nonetheless, the vast majority include brackets or linkages affixed to the chassis or frame that provide the three point arrangement or have a drawbar receiving aperture. 
   Many tractors, due to the specialized uses for which they are sold, do not come equipped with a three-point hitch assembly mounted onto the chassis or frame. These tractors are often too small in practice to pull the kind of implements (plow, cultivator, etc) that are fixed to three point hitches. Furthermore, they are often bought with other specialized applications in mind that do not couple to a three point hitch. Examples include ditch digging attachments, backhoe attachments, pavement breaking attachments, pavement cutting attachments, road grading attachments and the like. 
   One difficulty with such vehicles is the lack of a standard hitching structure that a variety of these specialized attachments or implements can be fixed to. The traditional three point hitch is large and often unwieldy on such small tractors, and a simple means of towing the implement, while necessary, is not enough to support the implement. 
   Several systems for attaching an implement to a vehicle are worth mentioning. 
   U.S. Pat. No. 5,779,429 illustrates a system for quickly attaching an implement to a tractor. This device includes an elongated rectangular channel to which four hooks extend upward. The device is fixed to the tractor and the implement rests on the four upwardly extending hooks. 
   U.S. Pat. No. 3,876,092 illustrates an implement connecting coupler mechanism that is structured generally as a four bar linkage having one bar coupled to the frame of the tractor and the opposing bar of the linkage configured to be rapidly connected to an implement. A hydraulic cylinder is coupled to and extends between the two links to permit the implement link to be raised and lowered with respect to the tractor. 
   U.S. Pat. No. 3,912,092 is directed to a tractor lift, including a tubular framework that is coupled to the free ends of a three-point hitch A scoop-shaped enclosure is pivotally fixed to the bottom of this framework. The scoop-shaped enclosure has a lip along its upper edge that is hooked over the top of the framework. 
   U.S. Pat. No. 4,986,722 is directed to a mounting structure for a loading attachment. The structure includes two opposing tubular extensions at the bottom front ends of a pair of tractor loader arms and a shallow upwardly facing trough at the top of the ends of the loader arms. An implement, here shown as bucket, has an elongated tubular section that is sized to fit in the trough. The implement is supported by the trough. When the arms are lifted, the bucket pivots inward toward the tractor along its bottom edge and has horizontal slots that engage the two opposing tubular extensions extending from the bottom of the free ends of the loader arms. 
   U.S. Pat. No. 5,088,882 is directed to a universal coupling for coupling a front end working member, such as a bucket or other implement, to the ends of the loader lift arms of a tractor. The implement includes two downwardly opening hooks extending directly from the surface of the bucket and two lower more widely spaced-apart eyes. The hooks engage a short tubular member fixed to and extending between two vertically extending spaced apart plates. The plates are spread apart at their bases and define two slots therebetween for receiving the eyes of the bucket. There are holes in the plates for receiving laterally extending elongate members such as pins, bolts or the like that extend through the plates and through the eyes to hold them together. In this manner, the bucket or other implement is fixed to the ends of the vehicle&#39;s loader arms. 
   U.S. Pat. No. 5,403,144 is directed to a blade tilt assembly for a front end loader. The assembly includes a generally flat plate that extends laterally and vertically with respect to a skid steer vehicle. The plate has a laterally and horizontally extending top edge and a bottom edge that supports pins that can be extended downwardly. This plate is fixed to the ends of the vehicle&#39;s loader lift arms to couple a bucket to the skid steer vehicle. A rectangular metal frame is fixed to the back of the bucket, sized to receive the plate fixed to the loader lift arms. The frame includes a downwardly facing slot that receives the top edge of the plate. It also includes two vertically oriented holes that receive the two pins extending from the bottom of the plate. In this manner the top and the bottom of the plate are fixed to the ends of the loader lift arms. 
   U.S. Pat. No. 5,685,689 is directed to a quick attach system for a front end loader. It includes a blade for a front end loader that has horizontally extending tubular structures along its upper edge. The blade also has two eyes extending outward from and away from the rear of the blade. The loader arms have a framework that receives the blade. This framework includes an elongate tubular member to which are coupled two vertically extending members on each end. These vertically extending members have laterally extending trough-like structures that cradle the tubular structures to support the tubular structures and the blade to which they are coupled. The bottom of the vertically extending members supports slideable pins that engage the eyes on the blade. 
   U.S. Pat. No. 5,779,329 is directed to a mechanism allowing quick implement attachment to tractors. It includes a framework of a laterally extending rectangular tubular member that is fixed to two vertically extending members at each end of the tubular member. These vertically extending members have hooks at their upper ends and lower ends that face upward to receive laterally extending tubular structures of an implement. The framework is fixed to the ends of jointed arms that extend outward from the rear of a tractor and hold the implement to the ends of the arm. Latches extending across the open tops of the upper hooks hold the implement in place. 
   U.S. Pat. No. 6,422,805 is directed to a quick coupler for bucket excavators. It is directed to a latch for latching to a tubular structure, for example, a tubular structure on an implement. 
   U.S. Pat. No. 6,533,319 is directed to a ballast attachment for attaching a ballast to a rear three-point hitch of a tractor. A rod extends longitudinally between the two lower arms of a three-point hitch. A downwardly-facing notch or groove in a ballast receives the rod and rests upon it. In this manner the three-point hitch supports the ballast. 
   U.S. Patent Application Publication Number US2003/0005605 A1 is directed to a mounting plate for quick attachment bracket and bucket construction. 
   None of the foregoing references provide an adequate system for coupling directly to the frame or chassis of a tractor or other work vehicle to support an implement. Most disclose structures that are not attached directly to the frame or chassis of the vehicle to provide a mounting point for implements, but are attached to the implements themselves, such as couplings for attaching buckets to the end of implements such as loader arms already attached to the vehicle—they do not disclose a way of attaching the implement itself to the frame or chassis. 
   What is needed therefore is a hitching structure fixed to the rear of a tractor&#39;s frame or chassis for coupling an implement directly to the frame or chassis of the vehicle. 
   What is also needed is a structure that can be attached quickly and with a minimum of effort to the rear frame of a tractor and to a variety of implements. 
   What is also needed is a structure having surfaces that are readily couplable to a variety of implements. 
   It is an object of this invention to satisfy the foregoing needs by providing a system that, in one or more of its claimed embodiments, solves the problems described above. It should be recognized, however, that not every arrangement claimed below addresses all of the needs and provides all of the benefits identified above. 
   SUMMARY OF THE INVENTION 
   In accordance with a first aspect of the invention, a quick attachment system for a work vehicle having a frame defining an upper pair and a lower pair of holes formed in opposing pairs of vertically and longitudinally extending frame plates, the upper pair of holes having a first common horizontal and laterally extending axis and the lower pair of holes having a second common horizontal and laterally extending axis, the system including a first elongate member extending between a nd coupling the upper pair of holes; a first hook that opens downward to engage the first elongate member adjacent a first of the upper pair of holes; a second hook that opens downward to engage the first elongate member adjacent a second of the upper pair of holes; a first eye having a first hole configured to be disposed adjacent to a first of the lower pair of holes; a second eye having a second hole configured to be disposed adjacent to a second of the lower pair of holes; and a plate that is coupled to and between the first and second eyes and the first and second holes. 
   The plate may be configured to extend generally perpendicularly to the longitudinal axis of the vehicle. The first hook and the first eye may be disposed on a first elongate member fixed to the plate, and the second hook and the second eye may be disposed on a second elongate member fixed to the plate. The first and second elongate members may extend vertically along the plate. The system may further include a drawbar, and the plate may include an aperture disposed along the lower edge of the plate that is configured to receive the drawbar and support the drawbar in a generally horizontal and longitudinally extending position. The plate may include a plurality of holes configured to receive threaded fasteners to fix an implement directly to the plate. The draw bar may be disposed to extend underneath the implement. 
   In accordance with a second aspect of the invention, a quick attachment system for coupling a drawbar and an implement directly to a frame of a work vehicle, where the frame includes two laterally opposed frame plates that extend longitudinally and are perpendicular to the ground, each of the frame plates having an upper hole and a lower hole disposed one above the other at the rear edge of the frame plate, and where the upper holes of the frame plates share a first laterally extending horizontal axis and where the lower holes share a second laterally extending horizontal axis, the system including at least a first laterally extending member coupled to the upper holes of the frame plates; at least a second laterally extending member coupled to the lower holes of the frame plates; a first hook that opens downward to engage the at least a first member adjacent a first of the upper pair of holes; a second hook that opens downward to engage the at least a first member adjacent a second of the upper pair of holes; a first eye having a first hole engaging the at least a second member; a second eye having a second hole engaging the at least a second member; and an implement mounting plate coupled to and between the first and second eyes and the first and second holes, the plate having mounting holes for attaching an implement thereto and an aperture for receiving a drawbar. 
   The mounting plate may extend perpendicular to the longitudinal axis of the vehicle. The first hook and the first eye are disposed on a first elongate member fixed to the plate, and further the second hook and the second eye are disposed on a second elongate member fixed to the mounting plate. The at least a first member may be a single cylindrical pin extending between and coupling the upper holes, and the at least a second member may include a first lower pin coupling the first eye to one of the lower holes of the frame plates and a second lower pin coupling the second eye to another of the lower holes of the frame plates. The system may also include a drawbar, and the mounting plate may include an aperture that is configured to receive the drawbar and support the drawbar in a generally horizontal and longitudinally extending position. The mounting plate may define a plurality of holes extending therethrough and the mounting plate may be configured to receive threaded fasteners to fix an implement directly to the mounting plate. The draw bar may be disposed to extend underneath the implement. 
   In accordance with a third aspect of the invention, a quick attachment system is provided for a work vehicle having a frame defining an upper and a lower pair of coupling holes formed in opposing pairs of vertically and longitudinally extending frame plates, the upper pair of holes having a first common horizontal and laterally extending axis and the lower pair of holes having a second common horizontal and laterally extending axis, the system including a means for coupling the upper pair of holes; a first means for engaging the first elongate member adjacent a first of the upper pair of holes; a second means for engaging the first elongate member adjacent a second of the upper pair of holes; a third means disposed adjacent to a first of the lower pair of holes for coupling to the first hole of the lower pair of holes; a fourth means disposed adjacent to a second of the lower pair of holes for coupling the second of the lower pair of holes; and a means for coupling the first second, third and forth means together and for attaching to and supporting an implement. 
   The first means and second means may include two parallel spaced-apart downwardly opening hooks. The third and fourth means include two parallel space-apart eyes. The first of each of the two hooks and two eyes may be disposed together on a first elongate member fixed to the means for coupling, and further, a second of each of the two hooks and two eyes may be disposed together on a second elongate member fixed to the means for coupling. The system may include a drawbar, and the means for coupling may include at least one mounting plate, and the at least one mounting plate may include an aperture disposed along the lower edge of the at least one mounting plate that is configured to receive and support the drawbar. The system may include an implement drawbar, and further the at least one mounting plate may include an aperture disposed along the lower edge of the at least one mounting plate that is configured to receive the drawbar and support the drawbar in a generally horizontal and longitudinally extending position. 

   
     BRIEF DESCRIPTION OF THE FIGURES 
     Preferred exemplary embodiments of the present invention are illustrated in the accompanying drawings in which like reference numerals represent like parts throughout. 
       FIG. 1  is a side view of a vehicle train, including a work vehicle having a hitching structure fixed to the rear of its frame, an implement mounted on the hitching structure, and a wheeled vehicle pivotally coupled to the hitching structure by a drawbar. 
       FIG. 2  is a perspective exploded view of the rear of the tractor of  FIG. 1 , showing the two plates that form the rear of the frame, the hitching structure, the pins that couple the hitching structure to the chassis, the ballast that is coupled to the hitching structure, and the drawbar that is coupled to the hitching structure. 
       FIGS. 3 ,  4 , and  5  are bottom, front and left side views of the hitching structure as it would be fixed to the frame of the tractor of  FIGS. 1–2 . 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Referring to  FIGS. 1–5 , a work vehicle, shown as tractor  100  in  FIGS. 1 and 2 , has a frame  102  to which a hitching structure  104  is mounted. An implement  106  (here shown as a ballast or counterweight) is fixed to the hitching structure. A drawbar  110  is also fixed to hitching structure  104  and extends rearward underneath implement  106  whereat it is coupled to the tongue  108  of a towed implement  112  (here shown as a four-wheel trailer). 
   Tractor  100  is a New Holland Model LV-70 tractor. It has a frame  102  that includes two elongated rearwardly extending members. These members extend both vertically and generally fore-and-aft to define two spaced-apart plates  114 , and  116  at the rear of the tractor. 
   Frame plates  114  and  116  each include two holes for mounting attachments to the vehicle. Plate  114  has an upper hole  118  and a lower hole  120 . Hole  118  is disposed vertically above hole  120 . Each of these two holes extends laterally through plate  114 , and each hole  118 ,  120  defines a generally laterally extending and horizontal axis. Plate  116  has an upper hole  122  and a lower hole  124 . Hole  122  is disposed vertically above hole  124 . Each of these two holes  122 ,  124  extends laterally through plate  116 , and each hole  122 ,  124  defines a generally laterally extending and horizontal axis. Holes  118  and  122  are coaxial. Holes  120  and  124  are also coaxial. Each of holes  118 ,  120 ,  122 , and  124  extends through semicircular protrusions from the generally vertical rear edge  125  of their respective frame plates. 
   The hitching structure  104  is coupled directly to frame  102  of vehicle  100  by an upper pin  126 , a left side lower pin  128 , and a right side lower pin  130 . Each of these three pins is fixed in place by snap rings  132  that are installed in grooves at both ends of each pin. These snap rings prevent the pin from being withdrawn once it is in place. 
   The upper pin is a laterally extending member coaxial with the two upper holes. While a single pin is preferred, separate pins or laterally extending members may be fixed to or engaged with the upper holes to support the hooks of the hitching structure  104 . 
   The lower pins are laterally extending members coaxial with the lower holes. While two pins are preferred, a single pin or laterally extending member may be employed to couple the eyes of the hitching structure to their respective lower holes. 
   The hitching structure includes two hooks, a left-hand hook  134  and a right-hand hook  136 , disposed on the left and the right side of the hitching structure  104 , respectively. Hooks  134  and  136  open downwardly to receive and be supported by a cylindrical structure (in this case upper pin  126 ) when the hitching structure is lowered down upon pin  126 . The internal radius of the hooks is nominally +25 mm, slightly larger than the 50 mm outer diameter of pin  126 . 
   The hooks are coaxial and parallel to each other. The inner radial surfaces of both hooks are defined by a laterally extending horizontal axis  138 . 
   When mounted on the tractor  100 , hooks  134 ,  136  face forward to engage the pin along the length of the pin that extends between frame plates  114  and  116 . Hooks  134 ,  136  are 30 mm thick as measured in the lateral direction. 
   Below each of the two hooks  134 ,  136 , are two corresponding eyes  140 ,  142  that are parallel to each other and in a spaced-apart relation. Eye  140  is disposed directly below hook  134  and eye  142  disposed directly below hook  136 . Holes  144 ,  146 , that define respective eyes  140 ,  142 , are coaxial, sharing a common laterally extending longitudinal and horizontal axis  148 . Axis  148 , which passes through and defines holes  144  and  146 , is directly below and parallel to axis  138  that defines the curved inner surface of hooks  134  and  136 . 
   Eyes  140  and  142  are secured to holes  120  and  124  by pins  128  and  130 , respectively. Pin  128  passes through and couples holes  144  and  120 . Pin  130  passes through and couples holes  146  and  124 . 
   Hooks  134  and  136  are spaced apart such that they both just fit between plates  114  and  116  with hook  134  adjacent to and abutting frame plate  114 , and hook  136  adjacent to and abutting frame plate  116 . Eyes  140  and  142  are similarly spaced apart such that they both just fit between plates  114  and  116  with eye  140  adjacent to and abutting frame plate  114  and eye  142  adjacent to and abutting frame plate  116 . The clearance between the hooks and eyes, and the plates is on the order of 0.5 to 2.0 millimeters. This close spacing prevents the hooks and eyes from sliding laterally and rubbing against the pins that support them. 
   In the preferred embodiment, left side hook  134  and eye  140  are formed from a single elongate member, here shown as a vertically extending elongate bar of steel  149 . Similarly, right side hook  136  and eye  142  are preferably formed from a single elongate member, shown here as a vertically extending elongate bar of steel  150 . 
   In addition to elongate members  149  and  150 , hitching structure  104  includes a vertically and laterally extending plate  152  to which member  149  and  150  are fixed (by welding in this case). Plate  152  has four through-holes  154 ,  156 ,  158 ,  160 , that are arranged in a rectangular pattern. The holes are laterally spaced apart about 320 mm and are vertically spaced apart 280 mm. 
   Threaded fasteners  162 ,  164 ,  166 , and  168  are inserted through these through-holes to fasten plate  152  (and hence hitching structure  104 ) to implement  106 . In the embodiment of  FIGS. 1 and 2 , implement  106  is a ballast used to anchor the rear wheels more firmly on the ground. 
   Plate  152  has a lateral width of 580 mm, a thickness of 20 mm and a height of 465 mm. This provides a suitable area for coupling an implement to, whether that implement is a ballast, such as illustrated here, a backhoe attachment, a pavement breaker, saw or other device. 
   Hitching structure  104  also includes a horizontal rib  170  that extends horizontally across the forward face of plate  152 . This rib is disposed generally perpendicularly to the surface of the plate extending outward and forward from plate  152 . It is fixed (preferably by welding) on each end to vertical hook and eye members  149  and  150 . 
   Hitching structure  104  further includes a vertical rib  172  that is also fixed (preferably by welding) to the forward surface of plate  152 . Rib  172  is disposed along the lateral centerline of plate  152  and is fixed (preferably by welding) at its upper end to rib  170 . 
   Hitching structure  104  also includes an upper drawbar coupling  174  that is fixed (preferably welded) to plate  152  just above the bottom edge of plate  152 . Drawbar coupling  174  is preferable formed as a single horizontally extending elongate member that is fixed (preferably by welding) to plate  152  and to vertical members  149  and  150  at each of the ends of coupling  174 . 
   Coupling  174  has a vertically extending hole  176  that passes through coupling  174  forward of plate  152 . Hole  176  is sized to receive a standard drawbar coupling pin  190  passing therethrough. 
   Hitching structure  104  includes a second drawbar coupling  178  that is also fixed (preferably welded) to a downwardly extending protrusion  180  of plate  152  just above the bottom edge of plate  152 . Drawbar coupling  178  is preferable formed as a single horizontally extending member. Coupling  178  like coupling  174  has a vertically extending hole  182  that is coaxial with and directly underneath hole  176  such that drawbar coupling pin  190  passing through hole  176  will continue on into hole  182 . 
   The bottom of plate  152  includes an aperture  184 , here shown as a slot, which is formed therein. This aperture is configured to receive drawbar  110  to which vehicle  112  or other implement may be coupled. 
   To couple an implement to the tractor, drawbar  110  is first coupled to hitching structure  104 . Drawbar  110  is an elongate member having an aperture  188  that is sized to receive a pin passing through holes  176  and  182  of the drawbar couplings. The forward end of drawbar  110  is passed through aperture  184  of plate  152  until aperture  188  is axially aligned with holes  176  and  182 . Once in this position, a pin  190  is passed through and retained in holes  176 ,  182  and aperture  188 . Pin  190  prevents drawbar  110  from being withdrawn from hitching structure  104 . The opposite end of drawbar  110  includes a second aperture  191  to which a towed implement  112  is coupled. 
   Drawbar  110  extends completely underneath the implement fixed to plate  152  (e.g. the ballast) and out from under the rear of the implement. In this manner, the rear end  192  of drawbar  110  can be easily coupled to various towed implements and also can be easily removed prior to the removal of hitching structure  104  from frame  102  of tractor  100 . 
   The combined vehicle in  FIG. 1  may be assembled as follows. First, the operator inserts upper pin  126  through holes  118  and  122  in plates  114  and  116 . The operator also fixes retaining rings  132  to both of the free ends of pin  126  to prevent pin  126  from slipping out of holes  118  and  122 . 
   The operator also attaches hitching structure  104  to implement  106  by passing threaded fasteners  162 ,  164 ,  166 , and  168  through holes  154 ,  156 ,  158 ,  160 , respectively, and threading them into corresponding threaded holes  196 ,  198 ,  200 ,  202  in implement  106 . 
   The operator then lifts combined implement  106  and hitching structure  104  and maneuvers the combined structure into position until the open ends of hooks  134  and  136  are disposed above pin  126 . The operator then lowers the combined implement and hitching structure until the root of hooks  134 ,  136 , rests on pin  126  supporting the weight of implement  106 . 
   Once a portion of the weight of the combined structure  104  and  106  is resting on pin  126 , lower holes  120 ,  124  of plates  114 ,  116  can be readily aligned with holes  144 ,  146  of eyes  140 ,  142 , respectively. This is true since the vertical spacing between holes  118 ,  122  and holes  120 ,  124  is the same as the spacing between the cylindrical root of hooks  134 ,  136  and holes  144 ,  146 , respectively. Resting hooks  134 ,  136  on pin  126  automatically aligns the lower holes with a modicum of implement pivoting. 
   With the implement pivoted into the proper position to align the lower holes, the operator inserts pin  128  through holes  120  and  144 , and inserts pin  130  through holes  124  and  146 . The operator then attaches retaining rings  132  to the free ends of pins  128  and  130  to hold them in the holes. 
   At this point, the implement is fixed to the rear frame of the tractor with one intermediate structure: hitching structure  104 . It cannot move relative to the tractor frame. It cannot be raised or powered by hydraulic cylinders or other adjusting devices. 
   With the implement in place, the operator can then release the implement (which has most probably been lifted in place by other mechanical means, such as a chain fall, crane, forklift, telehandler, or improvised lifting device such as the bucket of another tractor), and let the tractor support the entire weight of the implement. 
   With the hitching device and implement securely fixed to the back of the tractor, there is room for the operator to reach under implement  106  and insert drawbar  110  through aperture  184  of plate  152 . The operator slides the drawbar  110  forward until holes  176  and  182  are aligned with aperture  188  of drawbar  110 . 
   The operator then inserts pin  190  through holes  176 ,  182  and aperture  188  and secures the pin in place. 
   With the drawbar in position, the operator then attaches tongue  108  of towed implement  112  to the free rear end  192  of drawbar  110 . The entire vehicle shown in  FIG. 1  is now assembled and ready for transport. 
   While the embodiments illustrated in the FIGURES and described above are presently preferred, it should be understood that these embodiments are offered by way of example only. The invention is not intended to be limited to any particular embodiment, but is intended to extend to various modifications that nevertheless fall within the scope of the appended claims. 
   For example, while two upper hooks and two lower eyes are illustrated, two upper eyes and two lower hooks may be employed instead, or four upper and lower eyes, or four upper and lower hooks employed. 
   While the hooks and eyes are illustrated as parts of two vertically extending members, each hook and eye may be separately attached to the mounting plate of the hitching structure. 
   While there are four mounting holes illustrated in the figures, a mounting plate with no holes may be provided, for example, to attach the mounting plate to an implement by welding, or by using threaded fasteners that extend through the implement and thence into the mounting plate. Alternatively, several holes may be provided in the mounting plate, but they may be disposed in a different pattern unlike the rectangular pattern illustrated here. 
   The mounting plate, while shown here as flat, may be somewhat curved, for example to accommodate a curved cast portion of an implement. It may also be less than perfectly flat by defining mounting pads, lands, ribs or other structures rising above the surface of the mounting plate for engaging with similar pads, lands or ribs on an implement. 
   A variety of generally cylindrical structures may be employed in place of the pins shown herein, such as bolts, screws, or other threaded fasteners; spring pins; generally cylindrical nipples, cones or other protrusions that may be inserted into the upper or lower holes and mate with them.

Summary:
A system for quickly coupling a mounted implement and a towed implement to a tractor frame or chassis includes a hitching bracket with two hooks and two eyes that are fixed to the frame of the tractor and a plate that is fixed to the hooks and eyes to provide a mounting surface for the implement. The plate also includes a slot for inserting a drawbar that can be attached to a towed vehicle. The drawbar is positioned underneath the implement.