detent portion 62 by forming a step 120 and inclined surface 124 on the guide rib 86 and a corresponding mating step 130 on the adjacent end of the locking bolt clamp head 76 also an inner surface 140 of the other bolt guide rib 86 is inclined parallel to surface 124 the inclined surfaces 124 and 140 of ribs 86 88 respectively permit the locking bolt 72 to slightly cock clockwise when the bolt 72 is withdrawn fully outwardly and the mating steps 120 130 will latch the bolt clamp head 76 when the bolt is thus cocked clockwise cocking will occur because the curved geometry of the release shoulder 80 places the point of contact with the outward edge 96 of locking lever 90 below the center line of the compression spring 94 and the inward force of the spring thus creates a clockwise moment about that point of contact thus when the lock bolt 72 is fully extracted by pulling straight out on handle 108 it will cock and latch as shown in fig3 if the driver should then mistakenly push inward on the handle 108 the inward edge 98 of locking lever 90 will push against the rear face 82 of clamp head 76 creating a clockwise moment about the step 130 but the surface 140 of guide rib 84 would prevent the lock bolt 72 from further clockwise movement however upon the king pin 30 being separated horizontally the jaw 60 will pivot counter clockwise bringing the foot portion 64 into contact with the upper portion of clamp head 76 as shown in fig4 it will be seen in fig4 that the foot.