Push-to-connect fittings have several advantages over conventional compression style fittings. They are much faster to install, there are no loose nuts and sleeves to fiddle with during installation, and in tight spaces, no wrench is required when the tubing is attached. In addition, male pipe (NPT) parts have thread sealant pre-applied for convenience and further time savings. Users should be aware that many push-to-connect fittings are available on the market, but only D.O.T. branded fittings should be used in air brake applications. G7000P series are D.O.T. accepted for all air brake applications except lines from the frame to the axle and lines between towing and towed vehicles. For these applications, use G7000 series or use G4300 series with rubber hose.