What does the symmetry symbol look like?

• A. A circle with a cross in the middle
• B. Three horizontal parallel lines with the middle one longer than the others
• C. An arrow going to the top right at a 45 degree angle
• D. Two arrows going to the top right at a 45 degree angle

Answer: (B)

The symmetry symbol is represented by three horizontal parallel lines, with the middle line being longer than the others. This symbol indicates that features of a part must be symmetrical relative to a central axis. The use of this symbol in a technical drawing informs the fabricator that the dimensions on both sides of the axis must be equal and that the feature must be designed to be balanced around that axis.

In the context of geometric dimensioning and tolerancing, clarity is essential for manufacturing. The symmetry symbol conveys a specific requirement that allows engineers and machinists to interpret the design intent accurately, ensuring that the part will function as intended in its application.

By using this specific geometric symbol, it allows for clear communication of the design requirement, eliminating ambiguity that could arise if the information were conveyed in words alone. This precision is a hallmark of GD&T practices, which focus on enhancing the quality and accuracy of manufactured components.