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 a dodecameric ring-shaped structure located at one end of the T6SS sheath. May properly attach the pre-assembled sheath onto the baseplate and/or stabilize the sheaths tubular structure. Homododecamer. Interacts with TssB1 and TssC1. Interacts with TssK1 and TssF1. Deletion abolishes the secretion of Hcp1, Tse3 and VgrG proteins, all markers of T6SS activity.