Crane blocks or hook blocks are the complete components of the hoist, and it is linked to the crane by the rope pulleys/sheaves through the rope. Its design depends on the crane's purpose and concept design whereas rope pulleys or sheaves and hook assembly design will be the key factor to achieve customer requirements and expectations. Sheaves must keep a proportional relation and must be symmetric to the gravity centre of the crane block. Last decades, the sheaves diameter has decreased thanks to wire ropes advanced technology using more flexible wire ropes, reducing rope diameter and increasing strength thanks to very advanced materials, having decreased the historical factor (rope diameter (d1) x factor=sheave diameter (D).

The number of sheaves in the hook block will depend on the total WLL of the hook block and individual sheave WLL: falls are called to the twisted rope, whereas 1 sheave always has 2 falls, and 2 sheaves have 4 falls. The fall must have a certain angle for safety reasons: regularly the maximum angle is regulated by international standards. Proof Test Load (PTL) is being performed at Irizar Forge benches to be able to cover a full guarantee to the crane operator.