Pressurized Mating Adapters permit pressurized spacecraft to dock with one-another despite differences in the diameters of their docking mechanisms. They also provide passageways for crew, equipment and supplies.
An adapter similar to the ISS Pressurized Mating Adapters allowed the Space Shuttle to dock with Russia's Mir space facility. The first two conical, 8-ft. long devices for the ISS connect Unity to Zarya and provide a docking port for the Space Shuttle. Both adapters were integrated with Unity prior to its launch aboard Space Shuttle Endeavour.
The adapters have computers mounted externally for use in early command and control of Unity. Because they are pressurized and heated, they also serve as short, tunnel-like bridges that crews can use to go from one part of the ISS to another, as well as between the Station and spacecraft that are docked there.
Airtight seals are formed by devices that pull together, lock and seal -- a different method than the "bump-to-trip latch, then seal" procedure that most spacecraft use to dock.
Pressurized Mating Adapters are Boeing products, built in Huntington Beach, Calif. The tight seal that permits shirt-sleeved transit between ISS elements and spacecraft is provided in part by Common Berthing Mechanism technology.