The bayonet connector is not that simple; there's more to it here.

The sleeve-type connector consists of three parts: the connector body, the sleeve, and the nut. After the sleeve and nut are placed over the steel pipe and the connector body is inserted, tightening the nut causes the sleeve's outer end to fit snugly against the conical surface of the connector body. The inner edge uniformly bites into the seamless steel pipe, creating an effective seal.