Not all cranes have two hooks. Depending on the specific construction requirements and the structure of the equipment itself, some cranes are equipped with two large hooks.
Generally speaking mobile cranes are equipped with two hooks, fast hooks and slow hooks. However, the use of fast hooks on large tonnage cranes is very small. It is mainly used on small cranes.
The fast hook is generally a single strand wire rope, which is fast and efficient.
Slow hooks will depend on the weight of the lifting object, many times need to return to the site wire rope, in order to reach to be able to lift the goods. The largest seen is 7-8 times, mainly on the lifting of heavier goods.
Double hook cranes are generally large tonnage, a main hook, a secondary hook, double hook cranes can work with two hooks at the same time to maintain the balance of the lifted weight, but also a single use of work, small tonnage on the small hook operation, saving resources.