REFFLEX® does not unconditionally support the application of copper gaskets.
Without using a copper gasket the usual 2.0-mm brass-to-brass or 5.0-mm steel-to-brass connection (e.g. the connection to a pressure switch, manometer, compressor valve service port or oil level system) is perfectly safe and 100% gas- and liquid-tight.

Of course the surface of the fitting on the equipment to be connected with must be smooth. Only would the surface clearly show deep scratches or other irregularities, the copper gasket might be required. Please realize that some well-known disadvantages of copper gaskets are: The soft copper gets flattened during tightening the nut, the gasket’s outside diameter grows larger, and copper gets inside the thread of the nut. The inside diameter grows smaller and may even substantially block the orifice of the fitting or disables the proper function of the access valve depressor (if applied)

Best procedure:
During tightening the flare nut one may see the REFFLEX® fitting rotate a short distance along with the flare nut. Unscrew the flare nut over one or two full revolutions. Manually rotate the fitting counter clockwise as far as it initially went along with the flare nut. Next finally tighten the flare nut. Doing so radial tension in the hose is avoided and now both matching surfaces fit perfectly together.