into the ball release position as seen in fig3 b lever arm 142 pushes on short arm 128 a long arm 128 b also cooperates by pressing on lever arm 142 to pivot tongue 125 b out of housing interior 118 thus allowing pawl 125 to disengage with tow ball 15 this enables coupling 100 to be lifted off it will be noted that in the ball retaining condition tongue 125 b just needs to engage tow ball 15 anywhere below the centreline between the widest part of the tow ball and including its neck pawl 125 is mounted so that it is pushed by tow ball 15 and pivots out of the way to allow tow ball 15 to pass into ball housing 110 via aperture 112 a the weight of the coupling and any riser or other attachment allows the coupling to be simply dropped onto ball 15 with no precise guidance needed pawl 125 is automatically pivoted out of housing interior 118 when coupling 100 is dropped onto ball 15 in addition because of its bias pawl 125 immediately assumes a ball retaining condition which locks ball 15 in place lever 140 is activated to achieve a ball releasing condition lever 140 operates to release pawl 125 by pressing thumb catch 145 towards tubular member 170 described below causing pawl 125 to pivot and withdrawing tongue 125 b from ball housing 110 the automatic locking and the requirement for positive manual operation of the lever to release the coupling is an important feature of the invention riser 160 in the form.