Automatic coupling hook for three-point lifting connecting rods of a tractor, fitted with an opening blocked by a lock made from two parts articulated to one another. The lock 8 comprises a head 16 and is articulated such that the said head is inserted between a bearing component 20 of the hook and the coupled component 4 so that the centre of the bearing surface 17 of the head 16 of the lock 18 against the coupled component 4 and the centre of the bearing surface 18 of the said head 16 of the lock 8 against the bearing component 20 of the hook 1 are practically aligned with the centre 0 of the coupled component 4, so that the head 16 of the lock 8 operates in crushing and not in bending. <IMAGE>
