If there are multiple concentric circles, which circle should you apply the center mark to?

The most appropriate choice for applying a center mark in the case of multiple concentric circles is the outer circle. This is primarily due to best practices in technical drawing and drafting standards, where it is important to provide clarity in the representation of features.

When positioning a center mark, the outermost circle serves as a clear reference point for the center of the set of concentric circles. By marking the outer circle, you simplify the interpretation of the drawing, allowing viewers to easily identify the central alignment and the relationships between the various circles. Adding center marks to every circle can lead to visual clutter, making it difficult for anyone interpreting the document to focus on the key aspects without unnecessary distractions.

Moreover, the outer circle usually determines the overall dimensions and boundaries of the feature in a design. This encompasses the inner circles and helps in defining the spatial relationship of the object being represented.