The hook block (also called lower block) is the lower block of a crane pulley system. It contains one or more rope sheaves through which the hoist rope is guided, as well as the load hook for accepting the load. By multiple rope passes over the sheaves of the hook block and the upper head sheave on the boom, the load capacity is multiplied.
Tower cranes typically have 2–4 sheaves in the hook block, while mobile cranes and crawler cranes have 4–12 sheaves. A Liebherr LTM 1300-6.4 with 12-fold rope pass can nominally lift 300 tons — each individual rope carries only 25 tons. The more rope passes, the slower the hoist speed (rope speed ÷ rope multiplication factor).
Hook blocks are equipped with safety latches that prevent unintended unhooking of sling attachments. Ball slewing rings on the hook enable free rotation of the load. For personnel transport (work basket), stricter requirements apply to the hook block and rope routing in accordance with DGUV Regulation 52.