Intermediate baseplate protein. Involved in the tail assembly. Homodimer (PubMed:2403438, PubMed:19896486, PubMed:27193680). Interacts with gp7. Part of the baseplate macromolecular complex which consists of gp5, gp5.4, gp27 (central spike complex); gp6, gp25, gp53 (inner baseplate); gp7, gp8 (intermediate baseplate); gp9, gp10, gp11, gp12 (peripheral); gp48 and gp54 (proximal region of the tail tube). Present in 12 copies in the baseplate. Expressed in the late phase of the viral replicative cycle. Belongs to the tevenvirinae baseplate structural protein gp8 family.