In a mechanical drawing, which symbol is used to indicate diameter?

In mechanical drawings, the symbol used to indicate diameter is a zero with a line through it. This representation clearly communicates to the viewer that the dimension being referenced is a diameter, which is crucial for understanding the size of circular features in the design. Using this specific notation helps to prevent confusion with other measurements and ensures precision in the interpretation of the drawing.

The understanding of this symbol is vital for professionals in fields such as engineering and manufacturing, where accurate specifications are essential for creating parts that fit and function correctly. Other symbols mentioned in the options do not convey the diameter measurement; therefore, their use would lead to misunderstandings in a technical drawing context.