G-lok double ferrule tube fittings g-lok range of double ferrule fittings work on the proven principle of two ferrules swaging to the tube when tightened. As the nut is tightened the front ferrule swages on to the tube making a prominent leak-proof seal and the back ferrules makes a positive impressions on the tube. G-lok fittings are used in process control, instrumentation, hydraulic & pneumatics applications in chemicals & petrochemicals, fertilizers, power plants and other process industries. The range includes double ferrule (swagelok type).