in fig1 the tow - bar 1 has a hole 2 . the part of the tow - bar 1 that joins to the back of the associated vehicle ( not depicted ) is drawn as ragged to distinguish it from the free end which is furthest from the back of the vehicle and has a rounded outline . in the following description the term “ front ” applies to being nearer to the vehicle and the term “ rear ” applies to being further away from the vehicle to which the tow - bar 1 is attached . the tow ball 3 has a seating flange 4 and a stem 5 . the tow - ball 3 is secured with a spring washer 6 and securing - nut 7 that fit the stem 5 after it has passed through the hole 8 in the anchoring - plate 9 and the hole 2 in the tow - bar 1 . the bottom face of the anchoring - plate 9 is flat to engage the flat upper face of the tow - bar 1 . the rear of the anchoring - plate 9 is shaped to lie within the outline of the rear of the tow - bar 1 . the top face of the anchoring - plate 9 is flat . some tow - bars 1 are angled upwards forward of the tow - ball 3 ( refer fig2 ). the dimensions of anchoring - plate 9 are therefore set to ensure that when holes 8 and 2 align the front edge of anchoring - plate 9 does not extend forward of the place , if any , where the tow - bar 1 starts to bend upward . if this requirement is not met the flat anchoring - plate 9 is distorted when the securing - nut 7 is tightened and the flange 4 acts to bend the anchoring - plate 9 into a contour that matches the angled section of the tow - bar 1 . the anchoring - plate 9 has lugs 10 and 11 that extend down and fit snuggly alongside opposite sides of the tow - bar 1 . the lugs 10 and 11 have holes 12 and 13 respectively . the diameter of the hitching - pin 14 is matched to the diameter of the holes 12 and 13 . the lugs 10 and 11 are long enough to ensure that a hitching - pin 14 passing between the holes 12 and 13 will clear the underside of the tow - bar 1 . the shape of the lugs 10 and 11 is such that they do not interfere with a spanner tightening the securing - nut 7 on the stem 5 after it has passed through the hole 8 and the hole 2 . in addition the holes 12 and 13 are positioned in a manner that allows the hitching - pin 14 to pass between them without fouling the securing - nut 7 or the stem 5 . rotation of the anchoring - plate 9 , about the axis of the stem 5 , is limited by the lugs 10 and 11 embracing the sides of the tow - bar 1 . the inability of the anchoring - plate 9 to rotate on the axis of the stem 5 is retained even if the securing - nut 7 is not tight enough to generate sufficient friction between the anchoring - plate 9 and the tow - bar 1 to prevent one turning on the other . the foot - plate 15 has downward extending lugs 16 and 17 that have holes 18 and 19 respectively . the diameter of the holes 18 and 19 are matched to the diameter of the holes 12 and 13 and are positioned so that the hitching - pin 14 can pass through holes 19 , 13 , 12 and 18 when the underside of the foot - plate 15 is uniformly separated from the topside of the anchoring - plate 9 by a distance of 0 . 5 to 1 millimetre . the 0 . 5 to 1 mm tolerance between the foot - plate 15 and the anchoring - plate 9 allows subtle tilting of the foot - plate 15 about the axis of the hitching - pin 14 . the relevance of this tolerance and possible tilting relates to fitting the device to tow - balls 1 which have dimensions which vary slightly from that nominated by the manufacturer . see below for further details . the lugs 16 and 17 fit snuggly alongside the lugs 10 and 11 when the foot - plate 15 is linked to the anchoring - plate 9 by passing the hitching - pin 14 through the aligned holes 19 , 13 , 12 and 18 . the foot - plate 15 has a hole 20 that is centered over the hole 8 in anchoring - plate 9 when the holes 19 , 13 , 12 and 18 are aligned . hole 20 is sufficiently large to ensure that the foot - plate 15 can pass over the tow - ball 3 and the flange 4 . the hole 20 is also large enough to ensure that its edge cannot contact the flange 4 after the hitching - pin 14 has located in the holes 19 , 13 , 12 and 18 . tow - balls generally have dimensions that are specified by a government authority . some governments have safety design rules for tow - balls which mandate that the flange 4 has a larger diameter than the head of the tow - ball 3 . the government mandated dimensions generally have a manufacturing tolerance which is typically about 1 mm . the hole 20 is therefore made large enough to satisfy the size criteria listed in the immediately preceding paragraph , for the largest tow - ball dimension likely to be encountered for the nominated tow - ball size being used . permanently attached to the upper surface of the foot - plate 15 is a tube 21 . the walls of the tube 21 are located outside the perimeter of the hole 20 . in fig1 tube 21 has a square cross - section but a circular or other cross - section is satisfactory provided the walls do not encroach on the hole 20 . the top of the tube 21 has a platform 22 permanently attached to it . the platform 22 thus caps the top of the tube 21 . any desired attachment 26 can be rigidly linked to or articulated with the platform 22 by means that would be obvious to those skilled in the art . tube 21 is set to a length that ensures , that even if the locking - nut 7 is not attached , the tow - ball 3 can only pass up the tube 21 to a point where the stem 5 still protrudes sufficiently through the hole 8 to engage the hole 2 while the foot - plate 15 remains attached to the anchoring - plate 9 by the hitching - pin 14 being located across the holes 19 , 13 , 12 and 18 . after passing through holes 19 , 13 , 12 and 18 the hitching - pin 14 is secured in position with a retaining - pin 23 through a hole 24 in its end . the hitching - pin 14 can have a further suitably located hole 25 that accepts a padlock to deter removal of the hitching - pin 14 and theft of any of the illustrated components of the device . specific hitching - pin locks , which have been described by others , can also be deployed to deter theft . the lugs 10 and 11 on anchoring - plate 9 are made short enough to preclude the stem 5 from disengaging with the hole 2 whenever the hitching - pin 14 is engaged , below the tow - bar 1 , with the holes 19 , 13 , 12 and 18 . this arrangement ensures that it is impossible for the assembled device to separate from the tow - bar 1 even if the securing - nut 7 is absent . this arrangement also means that when the hitching - pin 14 is locked in position it is not possible to steal the device by undoing the securing - nut 7 . the rear of the tube 21 has a threaded hole 27 that accepts a setting - screw 28 that in turn carries a locking - nut 29 . the setting - screw 28 is critical to controlling rotation of the foot - plate 15 about the axis of the hitching - pin 14 . controlling this rotation stabilizes the position of the tube 21 relative to the tow - bar 1 . the setting - screw 28 is also critical to avoiding rattles between the foot - plate 15 and the anchoring - plate 9 and also rattles between the tube 21 and the tow - ball 3 . the integrity of the connection between the anchoring - plate 9 and the foot - plate 15 is assured whenever the hitching - pin 14 is permanently engaged in the holes 19 , 13 , 12 and 18 . the setting - screw 28 is only necessary to avoid undue rotation of the foot - plate 15 around the axis of the hitching - pin 14 . the setting - screw 28 is tightened just up to the point where no rotation of the foot - plate 15 , about the hitching - pin 14 , is possible . over tightening setting - screw 28 results in a constant compression force on the tow - ball 3 and this makes it impractical to readily insert and remove the hitching - pin 14 through the holes 19 , 13 , 12 and 18 . the setting - screw 28 is made only finger tight to eliminate rattles and is then locked in position with the locking - nut 29 . the setting - screw 28 may need readjustment at a later time if significant wear or distortion of the engaged components occurs with prolonged use . the setting - screw 28 does not perform the same function as the “ t ” locks ( parts 17 ) disclosed in new zealand patent number 226926 . those “ t ” locks generate constant compression forces against a tow - ball and thereby friction between the tow - ball and the “ t ” locks as well as friction between the tow - ball and the cylinder supporting the “ t ” locks . the stability of the device disclosed in the current application is not dependent upon friction between the tow - ball 3 and the setting - screw 28 . in addition the properly adjusted setting - screw 28 does not need to be tightened or loosened every time the tube 21 is engaged with or removed from the tow - ball 3 . this is totally different to the mechanism disclosed in new zealand patent number 226926 where the “ t ” locks have to be released and tightened each time that mechanism is attached to or removed from a tow - ball . when the tow - ball 3 has known dimensions , which do not vary between batches , there is no need for a setting screw 28 if the internal dimensions of the tube 21 , at the level of the head of the tow - ball 3 , is matched to the diameter of the equator of the head of the tow - ball 3 referring now to fig2 , this is a side view of the device fitted to a tow - bar 1 that has an angulated segment between the tow - ball 3 and the vehicle ( not illustrated ). the various components are numbered as for fig1 . the part of the tow - ball 3 and the setting - screw 28 that are inside the tube 21 are depicted with broken lines . fig2 clarifies how , with the hitching - pin 14 in place , the device cannot release from the tow - bar 1 , even if the securing - nut 7 is absent . fig2 also demonstrates how the setting - screw 28 can avoid rattles by tilting the tube 21 , about the axis of the hitching - pin 14 , and thereby simultaneously taking up any slack between the rear of the tow - ball 3 and the neighboring face of the inside of the tube 21 as well as between the underside of the foot - plate 15 and the topside of the anchoring - plate 9 . point a indicates the location where the underside of the tilted foot - plate 15 contacts the topside of the anchoring - plate 9 . it should be appreciated that modifications and alterations obvious to those skilled in the art are not to be considered as beyond the scope of the present invention . for example , any alternative means , such as welding , of securely attaching anchoring - plate 9 to the tow - bar 1 may be adapted . alternative means of attaching anchoring - plate 9 to the tow - bar 1 would be essential if the tow - ball 3 was manufactured as an integral part of the tow - bar 1 .