An exemplary adapter configured as a transition between a fitting and a fluid system component. In one exemplary embodiment, the adapter is configured as a transition between a compression fitting and a fluid system component. The adapter comprises a body portion, a compression portion, and a flange portion. A first end of the body portion is inserted into a port of the compression fitting and the compression portion compresses a resilient seal against a sealing shoulder of the fitting. A nut of the compression fitting engages the flange portion of the adapter to connect the adapter to the compression fitting. A second end of the body portion is connected to a fluid system component. The adapter provides a fluid tight connection between the compression fitting and the fluid system component without using a gasket ring or a locking ring of the compression fitting.