Forms the 160 nm long, sixfold helical, rigid tail tube. Binding to the entry receptor triggers structural rearrangements of the tail tube leading to ejection of the phage DNA into the host. Homohexamer (PubMed:25525268). Self-assembles into a long sixfold helical tube (PubMed:25525268). SPP1 virion tails are composed of about 40 stacked rings, and each tail ring is rotated by about 21 degrees relative to the previous one (PubMed:25525268). Interacts with the tail completion protein gp17 (PubMed:25991862). The tail tube is formed by the proteins gp17.1 and gp17.1* at a ratio of about 3:1. Produced by ribosomal frameshifting. Produced by conventional translation.