Block

Any assembly of pulleys on a common framework; in mechanics, one or more pulleys, or sheaves, mounted to rotate on a common axis. The crown block is an assembly of sheaves mounted on beams at the top of the derrick or mast. The drilling line is reeved over the sheaves of the crown block alternately with the sheaves of the traveling block, which is raised and lowered in the derrick or mast by the drilling line. When elevators are attached to a hook on the traveling block and drill pipe is latched in the elevators, the pipe can be raised or lowered. See Crown block, Drilling block, Elevators, Hook, Reeve, Sheave, and Traveling block.