Structural component of the short non-contractile tail. The tail complex is involved in viral genome delivery. Forms the 12-fold symmetric toroidal domain immediately below the connector protein gp8. Once the tail tubular structure is formed, the interface between gp11 and gp12 generates the proper environment to interact with the six fibers, each made of gp17 trimers. Interacts with head-to-tail connector protein gp8, the tail component gp12, and the fiber protein gp17.