Construction of the flagellum begins with the assembly of the transmembrane membrane supramembrane ring (MS-ring), the flagellar type 3 secretion system (fT3SS), and the cytoplasmic ring (C-ring) rotor complex. The proximal rod polymerizes on top of the MS-ring followed by the FlgG distal rod to span the distance between the peptidoglycan layer and the outer membrane. FlgJ, the rod cap, allows the growing structure to pass through the peptidoglycan layer through localized hydrolysis of the peptidoglycan (28). Once the distal rod has reached the outer membrane, formation of the periplasmic ring–lipopolysaccharide ring (P-ring–L-ring) complex simultaneously forms a hole in the outer membrane and dislodges the rod cap. Rod cap removal allows the hook cap (FlgD) to form on the tip of the nascent structure and to promote assembly of the hook by FlgE subunits.