Load hook

A load hook is forged and designed to open visibly under overload rather than break without warning. This toughness is a property of the material and its heat treatment. The German DIN 15400 series specifies materials, strength classes, capacities and dimensions; DIN 15401 describes the single hook.

One rule follows without exception: a load hook is never welded, heated or straightened. Each of these interventions changes the microstructure – the hook looks the same afterwards and behaves differently.

The single hook is standard on chain hoists, rope hoists and balancers. As a swivel hook it runs in a bearing so the load can align itself without twisting chain or rope. The self-locking safety hook locks automatically under load and can only be opened when unloaded. Double hooks (ramshorn hooks) are found on larger cranes where the load is slung on two legs.

Which type fits depends on the slinging: how often is the load attached and released, can it unload and unhook when set down, and does it need to rotate?

The rated capacity of a hook applies to a load seated in the saddle. If the sling sits on the tip, a lever arm acts for which the hook is not designed. The same applies to side pull and to slings that are too wide, wedge in the throat and force the hook open.

The safety latch prevents the sling from jumping out when the hoisting medium goes slack. It is not a load-bearing part and must not be loaded. A latch that does not close by itself counts as missing.

A load hook carries markings for manufacturer, size and strength class. The gauge marks for the throat opening are set on the new hook and the original dimension is recorded – only then can an increase be detected later. Care means a free-running swivel bearing and a working latch; paint does not belong on gauge marks and markings.

A hook is replaced by a part specified by the hoist manufacturer, including the suspension and the locking of the hook nut. When a hook has to be replaced is covered under discard criteria.