SPT symmetry-free and model-free averages of fibril-bound TRiC reveal extra density at the chaperonin’s apical tips. Each panel shows an end-on and a side view isosurface for a 3-D average of TRiC in complex with mhttQ51 fibrils, and corresponding 2-D projections (black/white). Independent sets from single tomograms are labeled A, B, C, D and E. Within each, the numbering (i, ii and iii) indicates mutually exclusive averages. The numbers of subvolumes contributing to each average are (A.i.) 7, (A.ii.) 10, (A.iii.) 13, (B.i.) 7, (B.ii.) 10, (B.iii.) 5, (C) 12, (D) 8 and (E) 12. All the averages show overall TRiC-like morphology with extra densities protruding beyond the apical domains of the chaperonin.