A coupling hook has a latch element extending from a pocket through a passage to block a coupling pin in the hook opening in the locked position. The latch element is arcuate and has opposed curvilinear surfaces one of which is engageable with a fulcrum in the vicinity of an opening in the pocket through which an actuating lever of the latch element extends. The other curvilinear surface is engageable with a fulcrum in the vicinity of the passage and has a notch engageable with a bolt in the pocket in the locked position of the latch element. The latch element may be displaced to a release position either by lifting and then pulling the actuating lever or by a coupling pin engaging the curved end of the latch element to urge the latch element to a released position.