What marlinespike seamanship tool is a device consisting of a pulley encased in a shell?

The term "block" refers specifically to the tool that consists of a pulley encased in a shell. Blocks are pivotal in marlinespike seamanship because they are used to change the direction of force applied to a line or to gain a mechanical advantage when hauling heavy loads. The shell of the block protects the pulley and provides a sturdy frame, while the pulley itself allows for smooth movement of the line, reducing friction and wear. This combination of pulley and shell makes blocks essential for rigging systems on boats and ships. The other options, while related to seamanship, serve different functions: a cleat is used for securing ropes, a sheave refers to the wheel inside a block that the line runs over, and a winch is a mechanical device for winding in or letting out a rope or cable.