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 TssB1 resulting in the stacking of cogwheel-like structures showing predominantly a 12-fold symmetry (PubMed:23341461, PubMed:29307484). The sheath contracts to provide the energy needed for effector delivery (PubMed:29307484). Forms a heterodimer with TssB1. Heterodimers assemble to form the sheat of the T6SS machinery (PubMed:23341461, PubMed:29307484). Interacts with TssA1 (PubMed:27288401). The C-terminal region is required for cogwheel and tubule formation. Deletion mutant shows a clear reduction in E. coli killing and a lack of ability to secrete Hcp1, VgrG1a as well as Tse3.