Range limit set in Gwyddion shows a multimer (shadowed — specs as previous recent posts) but measurements are a little larger than normally appears, for diameter, for segmented arm length thus, total size. Image below shows upper basic operations>range limit> upper 175 lower 100 and the CRD stand out much better in this image. I did measure the arm length to the center brightest are, presumably the N termini junction but in fact if the N termini are joined side by side, in a circle, then the size becomes more in line with other multimers from this same SP-D sample and the same shadowing procedure.

Another way to measure the arms is thinking about the N termini being attached side by side in a ring. This makes the segmented line measurements of the hexamers shorter, more in keeping with published data. It is not clear which is most accurate.

The image above is masked to remove black and dark in CorelDRAW then overlaid on the original black and white shadowed image.