 Two styles of connection are available for this arrangement – face seal, and barrel seal.Face seal connections are similar to the DIN regulator connection seal, and consist of an o-ring in a groove machined into the end of the manifold tube, which is clamped against the face of the valve port by a threaded component.Face seals are simple and rugged, but rely on tight connection for a reliable seal, and do not allow any adjustment for cylinder centre distance.