Core component of the H1 type VI (H1-T6SS) secretion system that plays a role in the release of toxins targeting both eukaryotic and prokaryotic species. Forms the sheath of the structure by assembling into tubules together with TssC1 resulting in the stacking of cogwheel-like structures showing predominantly a 12-fold symmetry (PubMed:23341461, PubMed:25305017, PubMed:22906320). The sheath contracts to provide the energy needed for effector delivery (PubMed:29307484). Forms a heterodimer with TssC1. Heterodimers assemble to form the sheath of the T6SS machinery (PubMed:29307484). Interacts with TagJ (PubMed:22906320, PubMed:25305017). Interacts with TssA1 (PubMed:27288401). Deletion mutant shows a clear reduction in E. coli killing.