A single sleeve (ferrule) compresses the tubing as you tighten the nut, creating a strong seal. The nut and sleeve are included. Fittings are also known as flareless fittings. They are brass for good corrosion resistance.Tube supports (sold separately) are recommended if you want to use the fittings with soft polypropylene and polyethylene tubing to prevent the tube from collapsing.Install plugs with a nut (sold separately) on the end of fittings to block the flow of air or water.NPTF (Dryseal) threads are compatible with NPT threads. Inline tees are also known as branch tees.