Structural component of the short non-contractile tail. The tail complex is involved in viral genome delivery. Forms the end of the tail, including the canonical tube, the nozzle, and the small extensions below the fibers. Once the tail tubular structure is formed, the interface between gp11 and gp12 generates the proper environment to interact with the six gp17 trimers. Interacts with head-to-tail connector protein gp8, the tail component gp11, and the fiber protein gp17.