SP-D dodecamer with what looks like side to side N termini binding between two of the four hexamers.
Image from Arroyo et al. supplement Figure 4b. (I placed the arrows at the juncture of two sets of N termini from hexamers).  The possible side to side N termini binding is more often seen in multimers but it looks pretty clear in this dodecamer.
Measuring the width of the much narrower N termini junction peak here also shows the LUT plots which identify a tiny peak before the largest peak (outside the N and C termini of the trimer). The tiny peak on either side of the side to side N termini association may be unique and it will be necessary to see whether the shoulder bump is actually part the LUT plots as seen in the most typical images, or if the N termini are side by side if actually in some cases a separate peak (as one can at least conjecture about here) is present on either side (black arrows).  The width of the N termini peak is only 9 or 10 nm where when the N termini are joined side o side as seen here but much wider (like twice) when the N termini are joined end to end (typical) and that number of nm is posted a couple different places on this blog.