Chaperone–usher pili are found on many bacterial pathogens; for example, in uropathogenic Escherichia coli, they are involved in adhesion to host tissues and biofilm formation. Hospenthal et al. now provide a detailed look at the composition of the pilus rod from individual subunits in a 3.8 Å resolution cryoelectron microscopy reconstruction. Each subunit interacts with five preceding and five succeeding subunits, forming the helical rod. Interestingly, almost half of the surface area of each subunit contacts other subunits and mutations in central positions of these contacting interfaces impair rod formation. Amino-terminal extensions, 10-20 residues long, provide strong hydrophobic interactions between neighbouring subunits. Furthermore, the subunits also interface through weak polar interactions, in particular between subunits not directly next to each other. This combination of strong and weak interactions enables partial uncoiling of the rod — for example, to withstand the shear forces of urinary flow — while retaining the structural integrity needed to keep the bacteria attached.