member 17 being bent upwards at 90 u00b0 to form a lug 18 adapted to engage in a notch 19 in the rim 15 of the cup 14 the finger 17 has two transverse extensions slightly set back in the radial direction from the lug 18 and having at their end a downwardly bent lug 20 near the inside surface of one flange of the yoke 8 a hinge pin 21 parallel to the axle 7 passes through respective holes in the flanges of the yoke 8 and in the lugs 20 spring means in the form of a compression spring 22 are provided to press the lug 18 of the finger against the back of the notch 19 the spring 22 is advantageously coaxial with the pivot 9 in a blind hole opening onto the bottom transverse face of the pivot 9 the top end of the spring 22 bears against the back of the blind hole i e against the pivot 9 fixed to the frame of the cart the other end i e the bottom end of the spring 22 bears against the interior of the finger 17 it can be seen that the spring 22 tends to raise the lug 18 by pivoting it about the pin 21 one end 23 of the notch 19 forms an end stop for the finger 17 this end 23 is a vertical edge adapted to cooperate with a conjugate vertical edge of the lug 18 so that.