A component of a tunnel-tube junction station was the tunnel-tube. These tubes, four in number for each station, stretched outward from the junction station. Their construction involved a servoframe covered by a pleated skin. At the end of each tube was an airtight iris-hatch, along with a hatch-mounted mouth capable of docking with other junction stations, starships, or building hatches. Furthermore, viewports were installed along the sides of the tunnel-tubes.