What is the term for an imaginary straight line that divides a shape into two equal halves in a cylindrical workpiece?

The term that accurately describes an imaginary straight line that divides a shape into two equal halves in a cylindrical workpiece is the "axis." The axis of a cylinder serves as a reference line that runs through the center of the cylindrical shape, extending from one end to the other. It plays a crucial role in machining operations, as many processes, such as turning or milling, use the axis for symmetrical operations to ensure uniformity and balance in the workpiece.

In the context of cylindrical shapes, the axis is central to the geometry and helps in defining operations around it, making it an essential concept in metal cutting practices. Other terms like centerline, diameter, and plane could imply different meanings or applications, which do not specifically relate to the concept of symmetry in this case. For example, the diameter refers to a straight line passing from one side of the cylinder to the other through the center, while a plane might not be limited to cylindrical shapes at all.