Structural component of the short non-contractile tail (PubMed:16452981). The tail comprises six spikes that mediate primary attachment to the host cell lipopolysaccharides (LPS) and display endorhamnosidase enzymatic activity, hydrolyzing the linkage between rhamnose and galactose of the O-antigen polysaccharide. Digestion of the LPS brings the capsid near the cell outer membrane (PubMed:20709082, PubMed:4633001).