(a) Our analysis of the CHO average suggested that several features, including the pinhead, were at less than 100% occupancy in the average. All subvolumes contributing to the whole-population average were classified based on the presence or absence of the pinhead, using a mask specific to the pinhead (dashed circle). (b) This classification yielded several classes, but the most populous class yielded an average that was enriched for pinhead-containing subvolumes. (c) A representative centriole refit showed that pinhead-containing subvolumes clustered together, suggesting that the centriole had distinct domains along its proximal-distal axis. Scale bar is 25 nm in (a) and (b), and 100 nm in (c).