Assembles to form the non-contractile sheath that surrounds the tail tube (PubMed:18374942). Allows viral attachment to the host by binding the bacterial outer membrane protein NfrA (PubMed:19011026). Interacts with host NfrA receptor; this interaction is essential for viral adsorption to the host. Present in about 6 copies in the virion. It is uncommon for short-tailed phages to have a tail tube inside a non-contractile sheath.