What is a lifting hook ?
A lifting hook is a device used as part of a hoist, pulley system, or other lifting system to secure loads for movement. The hook itself can vary in size, shape, and function, and most are made of a heavy metal such as steel. The lifting hook is likely to feature some sort of latch that snaps into place to close off the mouth of the hook; this prevents the rope or cable being secured by the hook from slipping off the lip and becoming unstable or completely falling.
Smaller hoist and lift systems will generally feature a smaller hook. The lifting hook can be secured directly to a cable or rope, though in some cases, the hook features some sort of chassis or frame that allows it to move freely and independently from the cable itself. This independent movement will prevent the cable from winding and potentially binding or breaking as the load being lifted moves. The hook will swivel instead, allowing the load to rotate without turning the cable itself. A swivel lifting hook is usually mounted on larger systems, though very small, light-duty hoists can feature such a swiveling device as well.
The shape of the hook generally looks like a J, and the lip will usually protrude slightly outward to protect the tip from getting caught on a rope or other materials being lifted. A gate will close the open end of the J, much like the gate of a carabiner used for rock climbing. The gate is usually spring loaded to prevent accidental opening during use, but is not itself a load-bearing device. It is meant simply to prevent the rope or cable from sliding off the hook during use.
Sometimes a lifting hook is designed for use with a chain. If this is the case, the hook is often secured to the chain using a cotter pin assembly. This system features a threadless bolt that slides through an opening on the hook; the chain can be fed around this bolt, and then the bolt is slid through yet another opening on the hook. Once in place, a cotter pin is slid through an opening in the bolt to ensure it does not slide back through the hook hole. These assemblies are easy to use and generally fairly reliable, though the cotter and pin will often need to be large depending on the size of the hook itself and the weight capacity for which it is rated.