What symbol is drawn when a hole has been engaged during an operation?

The symbol used to indicate that a hole has been engaged during an operation is a circle. In engineering drawings and engineering practices, circles are commonly used to represent holes. This convention helps convey information clearly and allows for universal understanding among engineers and technicians. The circle not only indicates the presence of a hole but is also informative regarding its size and location within the design. Using a circle for this purpose is standard practice in technical drawing, ensuring that all parties involved can accurately interpret the specifications and ensure that the correct operations are performed.

The other options do not serve this function; triangles, squares, and rectangles typically represent other features or aspects in a drawing, such as different types of shapes or sections, but do not denote the presence of holes.