Tube Fittings are designed, manufactured, and quality controlled to be totally "interchangeable" with the Swagelok brand of tube fittings.The double ferrule design, with the staged sequential swaging action of the ferrules during make-up, Back ferrule make a grip on tube & front ferrule work as sealing on tube, compensates for the variation in tubing materials, hardness, and thickness of the tube wall to provide leak-tight connections in an extensive range of applications.