Brennan Industries” double-ferrule, instrumentation-grade tube fittings provide leak-proof and torque-free seals at all tubing connections. The fittings are designed to reduce the chance of hazardous and expensive leaks in instrumentation, process, pneumatic, hydraulic, gas, and other tubing systems. The fittings consist of the nut, the back ferrule, the front ferrule, and the body. When installed they provide a five-piece connection with the addition of the tubing providing a solid leak-free joint. The two ferrules are tightly swaged around the tube and the lack of initial strain on the tubing ensures no tubing wall damage. Leaks are prevented because there is an axial movement along the tube instead of a rotary motion creating the joint. This axial movement prevents torque from being transmitted from the fitting to the tubing. Resistant to temperature change, the fittings do not significantly reduce flow area and work with a variety of tube materials. In addition, the two-ferrule action supersedes variations in the wall thickness, hardness, and dimensional tolerance of the tubes, ultimately compensating for most variables that lead to failure with other fittings. Brennan double ferrule compression tube fittings can be remade several times and can withstand heavy impulse and vibration in both vacuum and pressure systems. Requiring no special tools for installation or torque for initial makeup and using only geometry, the fitting requires 1.25 turns until it is tightly fitted.