 Though not a part of the main truss, the Z1 truss was the first permanent lattice-work structure for the ISS, very much like a girder, setting the stage for the future addition of the station's major trusses or backbones.It is made from stainless steel, titanium and aluminum alloys.While the bulk of the Z1 truss is unpressurized, it features a Common Berthing Mechanism (CBM) port that connects its nadir to the zenith port of "Unity" and contains a small pressurized dome that allowed astronauts to connect electrical ground straps between "Unity" and the truss without an EVA.