What is a double pulley with a center plate called?

The correct term for a double pulley with a center plate is known as a "Block." A block typically consists of two sheaves arranged on a common axis and held together by a central plate, allowing for effective pulley operations. It is a crucial component in rigging systems where mechanical advantage is necessary to lift heavy loads.

In terms of the other choices, a sheave refers specifically to the wheel or disk that the rope runs over but does not include the entire assembly of the pulley system. A becket typically refers to a fitting that can be used with a line or rope, often attached to the block but not the assembly itself. The term "pulley wheel" can refer to individual wheels that may be part of different types of pulley systems but isn't the standard terminology for a double pulley with a center plate. Thus, understanding the terminology associated with blocks and their components is essential for navigating concepts in mechanical systems and rigging effectively.