Today the market in a variety of fittings are presented for metal systems. Talking about how adherence to the tube should be divided by all the fittings on the screw (threaded) and media (press fitting).
In the first case the connection is achieved through the pressure that arises when tightening the nuts on an open ferrule. The figure shows the device of one of the threaded fittings company Pex Al Pex . To seal its tip has a special retention profile with the radial notch and the two O-rings, immediately adjacent to the pipe. Tight connection fitting body with a tip is a special seal. Another gasket is placed between the tip and the end of the pipe. This piece, which eliminates direct contact of the aluminum layer with a metal fitting and thus prevents the electrochemical corrosion, it is usually made of Teflon. As the seals are also recommended teflon gaskets.
As already mentioned, mounting screw connection does not require a special tool: it is made with two wrenches (one nut is tightened, and the second is resistance). To facilitate the introduction of the sealing rings and extend the life of the fitting, use silicone grease. It is prohibited to use mineral oil or other petroleum products. Typically, grease is a range of products produced by manufacturers of PEX pipe.