It prevents the inadvertent unlocking of the clamp due to vibrations or an accidental attempt of loosening / opening of the clamp. To open and release the toggle clamp from the locked closed position, press the lever arm and safety hook lever arm together (one hand operation).
.These widely-used steel on steel bushings are popular replacements in applications such as bull dozer cylinders, shovel-loaders, center pins, axial plunger pumps, tractor shovel cylinders, rock crushers, cranes and more.