The Common Mechanism (CBM) connects habitable elements in the US Orbital Segment (USOS) of the International Space Station (ISS). The CBM has two distinct sides that, once mated, form a cylindrical vestibule between modules. The vestibule is about 16 inches (0.4 m) long and 6 feet (1.8 m) across. At least one end of the vestibule is often limited in diameter by a smaller bulkhead penetration. The elements are maneuvered to the berthing-ready position by a . Latches and bolts on the Active CBM (ACBM) side pull fittings and floating nuts on the Passive CBM (PCBM) side to align and join the two.